I agree that ERML is maybe too good and it's indeed the ingredient of every good Clan build out there. It's somewhere between the IS LL and IS ML, but rather closer to the LL. It's an unpopular opinion, but I think the ghost heat limit for the C-ERMLs should be decreased to four, to make it more comparable to the IS ML in terms of damage output (RIP Nova).
Clan SRMs are indeed straight upgrades on the paper. Though I don't know if you played with them much, but the non-Artemis spread is just unbearable. Like LBX at 300 meters unbearable. You have to take Artemis, which brings their tonnage closer to the IS counterparts. Even then, the spread is still not good.
C-ERPPCs are indeed good. I find them to be good killers because the arcing damage tends to reach to the open components (arms, XL side torsos) you missed. The lack on a PPC option though is the trade-off. At 15 heat, even the 30+ heatsink builds struggle to cool these things to sustain fire. When fighting anything with C-ERPPC you just have to get them to alpha 1-2 times and then just hug their faces while they heat manage.
Clan Ballistics are . . . decent, but need some love. C-UAC2 is as worthless as the AC2, but at least it can fulfill its role envisioned by the mighty Paul as a suppression weapon unlike the AC2. C-UAC5 is horrible when taken as a single weapon but transforms to a murder machine when you bring two or more. C-UAC10 is the best of them as a single weapon, but this is when you begin to have troubles aiming because of the slow projectile speed. C-UAC20 is devastating when you're actually face hugging something, but otherwise tedious to aim at moving targets at other ranges. The thing is, PGI can only buff them so much because of the boating potential. Any buff will be "exploited" by 5-6 ballistic Dire Wolf builds. Still, I heard PGI is going to buff UAC projectile speeds, so the help is on the way.
The Clan XL engines as most people I'd say agree, bring all of the good of the XL engines while having none of the negatives. You die when you lose two torsos and coincidentally you're useless after you lose two torsos in 99% of the 'Mechs, so it won't matter. The tanking potential argument is baseless as no good team/player will keep shooting at a disarmed 'Mech in combat. People demanded more penalties for losing side torsos, including reduced speed, but PGI only made you lose 20% of your internal heatsinks in addition to the DHS you lost in side torso destruction. Did that make any difference? In my experience, hardly.
About the IS quirks, I think the idea was to bring underpowered chassises to "Tier I" IS 'Mech effectiveness like the old Victor, CTF, Shadowhawk and Jenner instead of simply making them Clan murder machines. When they "accidentally" buffed some of them to the point they could actually duke it out with the best Clan 'Mechs, they were promptly nerfed.
One thing to consider is that while the weapons may be better, some Clan 'Mechs are so horribly designed that they can't take advantage. Since we can't change Endo&Ferro and locked components, it's a huge lottery each time PGI introduces a Clan 'Mech. Their fates are usually decided by their upgrades and locked components. The Summoner is shafted by its locked components and a lack of Endo while building for the Warhawk is like playing tetris with its 7 locked external DHS. Yet, you have Timbers, Crows and Dires on the other side with nearly perfect layouts that ooze every bit of Clan equipment advantage.
To be honest, I think even PGI is conflicted about if the Clan stuff should be better or comparable. They deliberately left some Clan stuff underperforming while also deliberately made the other part overperforming. Comparing the best with the best, I think the Clans come out on top. With the Wave 3 'Mechs which all come with awesome stats, they'll be even better (maybe not the Executioner).
TL;DR: Clan lasers are ridiculously good, C-ERML is problematic, C-SRM/LRMs are meh, C-Ballistics are meh (unless you boat them), Clan XLs are straight-up better. Not all Clan 'Mechs can take advantage of these.