Actually there'd be more difference than that. An AC/20 delivers 10 times the damage of an AC/2 at a fraction of the range, provided you can get all the shots to land for the AC/20. The reason for the AC/20's terrible range is a mixture of incredible firing rate, high recoil, and the fact that while AC/20s can vary from 30mm to 185mm for the IS, the AC/2 goes from 30mm to 90mm, so some AC/20s fire shells bigger than an AC/2 can ever hope to wield.
AC/2s have advantages in longer range because at most they only need to fire 10 shots, or 2 at its largest caliber. An AC/20 needs anywhere from 4 to 100 shots to net its damage depending on the caliber. Then there's the styles, there are burst fire ACs, chain fire and auto fire (yes, there is a difference, in this case chain fire is steadier and unlikely to jam and is usually accompanied by more than one barrel; lower calibers are likely to use this when needing to fire large volumes in a short period of time. Auto fire relies on the backblast or recoil of the gun to eject the old casing and chamber the new round. These are likely to have different issues when pushing them through the TacOps Rapid Fire Autocannons rule, which allows any standard AC to be used up to two ratings).
From there you have direct hit and glancing blow rules, which gives us some flexibility in damage across calibers and types, since we've basically changed our AC count for standard ACs from 4 different weapons to something close to 80 different weapons within 4 generic categories...and that's not counting what that change does to UAC and LB-X as well.
Of course, since autocannons are canonically fully functional up until approximately 2,000 meters where bullet drop will typically drop 'em, the longer your accurate range is the more relibly you can hit your target at long range. A tabletop pilot with the Sniper skill (something you would 'earn' in a game like MWO through practice firing long range until you 'git gud' and not a stupid unlock) can land shots at Extreme Range (960 meters) *2 which is 1720 meters at same challenge in difficulty to hit as a typical pilot without that gunnery skill can at 960 meters. Also keep in mind the tallest Battlemech or Omnimech in 3050 is 14.4 meters... Yeah.... Consider that.
The IS wouldn't be "inferior" because of range, as skilled players can overcome accurate ranges and nail enemies as far as they can see them. Sure they might be delivering glancing blows more often than regular or direct ones, but hey so would the Clans at those extreme ranges.
I admit that accuracy in tabletop is an issue. In fact it's a bigger issue than in MWO. Ever notice how in tabletop you can't "aim" or call out a specific body part unless the enemy pilot is unconscious or the enemy mech is completely immobilized (shut down, prone or on its back)? Easy: ToHit is affected by both your movement and the enemy's movement. In fact the more either of you move, the worse your aim is much like MWO. Except in MWO it's easier. In Battletech, the 'randomness' of where you hit is also attributed, even on aimed shots, to the fact that if the pilot is conscious, he can react to you by torso twisting, by throwing his arms in the way of your shots, by lifting a leg a little higher to catch the shot. In some examples of lore, some more skilled pilots are known to "Skip" like a kid.
The Diagonistic Interpretation computer included on every Battlemech is specifically mentioned that it tries to avoid all potential damage to the mech by automatically reacting to incoming from tree branches to potential collisions with buildings and street lights, to incoming fire. It's not fantastic at it, but it is always making the attempt. The exception is when the pilot intends to endure that damage or is more focused on what he is doing (such as aiming to make a shot,
trying to hold a door, etc.), this is the only time that a 'Mech does not try to automatically evade.
So, accuracy is a thing and it's a bigger thing in tabletop which if brought here, would be that much bigger of at thing than the joke that has been in every mechwarrior video game. Which yes, I suppose we can't blame PGI. Implementing such is difficult.
However even with just the DPS mechanics and an automatic 'conversion' if you target the enemy via StarSiege where weapons do not converge if not targeted and converge if targeted... things could go a long way in both tactical depth and accuracy 'merits' as well as 'difficulty' while still being very obvious the first time a player targets an enemy.
Damage spread would also be a bigger thing, larger weapons would spread more. And sure, lighter weapons are significantly weaker but that's why players bring them in numbers.
The problem is with MWO's mechanics, you have this issue...
Can't find the video, but basically they loaded a mech with MGs in Mechwarrior 2 Mercenaries and it was doing 60 damage per second, basically instakilling anything and everything they shot at. Yes we have hardpoint limits but MWO's excessive need for hardpoints is giving us this situation anyway in addition to the issue of accelerated damage through firing rates.
There's also the heat thresholds, which across past Mechwarriors ranged from 30 to 60. Here the current 'practical' height of threshold with the old skill tree is 129 if you're Clan and barely above 110 if you're IS. This is because PGI realized their firing rates cause extreme amounts of heat and thus gave heatsinks a threshold instead of just cooling. The trouble is unlike the Heatsink Taxing rule which does in fact give heatsinks a separate threshold, PGI put it into mech threshold to allow us to do massive amounts of alpha strikes.
So uh, you sure it'll be worse? It seems really bad.
Heatsink taxing has the potential to melt your heatsinks if you exceed their cooling power by a certain amount within 10 seconds. 30 threshold is really difficult to hit unless you're using PPCs or a large number of large weapons or alpha striking. (which I define as firing all your weapons at maximum output at the same time, so if your large laser takes 2 shots to deliver its damage and your medium laser needs 3 shots... if you alpha strike, all your energy weapons fire a single blast for full power and your ACs blast away and extra heat for all. Not to mention you wouldn't be able to use anything for 10 seconds if you were even still powered.)
So, alpha strikes meaningful yet 'gone' from traditional play. Laser vomit reduced in damage output, AC output reduced but made more even between IS and Clan, AC and UAC (UACs don't have the risk of blowing up if you push them unlike ACs, also ACs have a higher risk to jam if pushed as per the TacOps rapid fire autocannons rule.)
But wait, I hear you say, doesn't this mean that MGsare a useless 2 damage too and now DPS based?! Yes, why yes it is! Well except the useless. Nothing says a weapon ahs to fire all across the 10 seconds. An MG could actually be firing for maybe 2 seconds to deliver 2 damage and spend the rest of the time cooling off. Or akin to the RAC mechanic in MWO, the longer you hold it the higher its weapon heat gauge gets and when it gets too hot it'll cut off, so in theory if there's no cap to its damage potential and you give it time to cool off, you have "Burst Fire MGs", the Tac Ops rule which allows you to take an MG and fire in several bursts to net higher potential damage in a turn, though it generates heat and could jam.
Oh wait, lore has it that MGS in several instances are known for overheating and jamming. Not in tabletop because the heat isn't significant enough for heatsinks and is air cooled unless pushed too hard via the burst fire MG rule, and jam risks are only on some brand names and as such just have the ammunition feed design quirk unless using the burst firing rule in which the heat can cause a jam.
Then there's minimum range...
In tabletop and Battletech Lore, firing below minimum range doesn't magically do zero damage like MWO. Instead, it does full damage. It's just harder to do because the closer a target is, the more significant its movement is compared to yours. Watch something fly by like a plane. Notice how slow it seems? It's going an average ground speed of 600 mph, that's 965.6 kph. The farther something is, the less you have to move to hit it. So why don't AC/20s land shots farther away? AC/20s fire 30mm to 185mm for the IS, while AC/2s fire 30mm to 90mm.. Meaning if you used the same ammo in each, the AC/20 basically fires 10 times faster. Now try to keep that recoil on target.