Point 1 - clan tech is too light and takes too few slots. This is not offset enough by the negatives. Clan mechs can pack an obscene amount of firepower. Let's take a look at the pod space per mech:
Kit Fox - 14.53 tons of pod space, 27 free slots
Adder - 15.8 (16) tons of pod space, 28 free slots
Nova - 15.5 tons of pod space, 34 free slots, 4 DHS and 5 JJs hard wired (which is not a negative at all)
Stormcrow - 22.86 (23) tons of pod space, 33 free slots
Summoner - 20.69 (21) tons of pod space, 35 free slots, 4 DHS, 5 JJs hard wired (chassis suffers somewhat from a lack of hardpoints)
Timberwolf - 27.46 (27.5) tons of pod space, 33 free slots, 5 DHS hard wired
Warhawk - 32.3 (32.5) tons of pod space, 26 free slots, 10 DHS hard wired
Direwolf - 50.31 (50.5) tons of pod space, 41 free slots, 5 DHS hard wired
With clan equipment taking way less tonnage and crit slots, only the sky (hardpoints) is the limit. Case in point:
Warhawk - Firepower 83.7; sustained DPS 7.03; HE 36%
Stalker - Firepower 77.7; sustained DPS 3.29; HE 17% -
WHK has more range on the ERLL, twice the range on CMPL, more speed, way better HE (Smurfy accounts for GH on HE), while the Stalker has 12 more slots left (yay)
Stormcrow - Firepower 44; sustained DPS 5.62; HE 43%
Shadowhawk - Firepower 41.8; sustained DPS 5.35; HE 43%
Stormcrow has nearly twice the range and damage on the ERSML, better speed and agility, more survivability through its XL, no worries about ammo locations and can fire its CUAC10 twice within the burn time of its lasers, giving it scary 54 damage dealt within one second of engagement in SRM range
These were just examples where I compared mirrored builds. Clan mechs can pack a lot more punch than any IS mech if it doesn't want to equip a ridiculously small engine. Which leads us to
point #2:
Clan weapons do too much damage at way too low weight and crit slots.
CERSL, CERML and CMPL offer way better damage to heat ratio, damage and range than their IS counterparts. Clan large laser variants are somewhat more in line, but still offer too good performance across the board, despite their "drawbacks". Holding the laser on target for the duration is a thing you can practice and adapt to, though I admit that CERLL have some problems at range.
Clan missiles (except streaks) are way too good. Across the board they way only half the tonnage, SRMs have no drawbacks at all while LRMs will have their ripple fire mitigated by the ability to do damage below 180 meters. I have to admit I really like their flight path, they work like LRMs used to in closed beta. Giving that flight path to IS LRMs as well would make a damage buff possible.
Clan ACs weigh less and take less slots than their IS counterparts, CUACs also have lower jam chance. Burst fire is only a problem at ranges 400+, while below that their ability to fire twice within one cooldown cycle mitigates the pin point advantage of the IS. Up close and personal they are outright stronger. Clan Gauss have no drawbacks at way lower weight and less crits.
CERPPCs have 50% more damage at lower weight and crits, no drawbacks.
Point 3 - supposed drawbacks of clan tech and mechs
Clans got some unique traits in order to compensate for their superior range, less weight, superior damage and less slots. These do not work out as such. Laser duration and some pod quirks work to lengthen cooldown times, especially on lasers. This is mitigated by "Fastfire" and in the game environment is even helpful for heat dissipation. Most of the times actual combat is not even affected by this at all! Combat in MWO consists of positioning, avoiding/tanking damage, lining up the shot and firing. These actions get repeated with every weapon cycle and take usually more time than the actual weapon cooldown. Only on few occasions like brawls or for some shots out of a safe position is it even possible to fire as soon as the weapon is ready. It's still only lengthened by fractions of a second and can be adapted to with a little bit of practice. Overall DPS of clan weapons still stay superior.
Some pods also have quirks reducing torso twist rate, which is not to be mistaken for twist speed. This quirk is also mitigated by eliting the mech, superior mobility etc.
Point 4 - Engines hinder clan mechs from being great
No, they don't. With exception of three of the
currently available mechs, clan mechs use one of the best options, granting them superior mobility and survivability while giving more than enough pod space to pack twice the damage of an IS mech, at the same or even better HE. Clan XLs have no drawbacks, even when they lose two engine slots.
Oh, and have I mentioned free CASE everywhere already?