Short of 'laser vomit', say boatloads of ER MLs at 6 at a time with previous DHS capacity, Clans have been a joke for a while. Clan autocannons were worse, but no one would use them because they spread so much, and IS had and still has the only "one shot kills all" weapon combination (twin AC/20s).
Dire Wolf? 1 shot.
Timber Wolf? 1 shot.
Stormcrow? 1 shot. (If they hold still or slow down enough; that bouncy cockpit's hard to hit).
"Pro Clan Skillz?" 1 shot.
IS wins. 28 tons + ammo.
Clan's weapon combination with similar effectiveness that doesn't instantly blow you up? 13 ER PPCs. Only thing they have that compares. 78 tons plus heatsinks. (Strange that 13 ER PPCs won't instantly kill you, but 5 ER PPCs will, and 4 ER PPCs is near suicide and often still won't do what twin IS AC/20s will). Just be prepared to
sit for 3 minutes if you don't want to die.
So I wouldn't go worrying about that "ton" problem.
The Clan laser vomit issue has been significantly reduced by changing DHS thresholds. Clan heatsinks can't handle as much heat overall (by 0.1 unit less per DHS), but each cools 0.01% faster per second than IS DHS, rendering Clan weapons to be more DPS oriented requiring more 'face time' while IS weapons are more "Pop and shoot" oriented, allowing IS mechs to spread damage, aim in to deliver devastating damage and then spread again.
(Edit)
I would like to add this:
Clan mechs are DPS oriented, requiring more skill to keep crosshairs on the target while firing (which can be harder than one might think). This does allow some opportunities that IS doesn't have, like partial "grazing" damage delivered by autocannons, or LRMs that stream fire so when the first tidbit doesn't hit the rest might (unlike IS where if there's an obstacle they all probably didn't hit). Keeping crosshairs perfectly on target is more difficult at range, which is ironic since the main Clan advantage is range. Sure, Clan lasers also do more damage, but those longer beam times actually reduce firing frequency, and in the end the amount of damage they do over time in a 10 second cycle compared to unquirked firing rates is barely superior. Against quirked firing rates, either on par with weaker quirks or clearly inferior against the more moderately quirked firing rates.
IS mechs are focused on heavy damage in tight spots. Their pop and squat style of weapons would be great at range, except IS generally lack range (it is great against Clan range though to pop out and hide before the barrage hits). IS mechs without quirks already have superior firing rates, but with quirks included their firing rates help better equate damage potential. Many IS mechs in the missile department can almost double the damage output of Clan counter parts within a short amount of time, furthermore the quirked IS autocannons can nearly rival "UAC" double-tap damage if the UACs didn't jam; once you factor that in... it's GG Clans, IS is OP.
The problem here is pretty simple. Getting close enough to deliver the damage. That is the only thing the IS has to figure out, and that boils down to player skill.
IS needs to Get Close to Devastate! Ambushes work. Some sneaky craftiness like the IS is canonically known for, such as getting in behind the Clans and taking them out from both sides works wonders if done effectively against unwary Clanners. Often, Clan mechs built for laser vomit can't "keep it up," and so once a Clanner fires 2 or 3 times in succession, RUSH because they can't do **** to stop you! And Dire Wolves? Run circles and laugh. Or heck, just stand on its head and kill all its teammates.

Ride the enemy, shoot his teammates. Or in this case, I was used in order to create a 5 AMS walking death machine and to allow the Adder to "Sharp shoot" over canyons without being on the canyon.
Far as XL engines, even without the penalties for losing a third of the engine, Clan mechs have significantly larger side torsos on ~most~ mechs than any IS counterpart. Stormcrow's about the only exception, but lets be honest if you're not shooting the legs of a Stormcrow then you deserve what you get. They're so big, they're so weak, it's so easy!
Edited by Koniving, 02 January 2016 - 04:56 AM.