I have used AP Gauss Rifles as being intro'd early; but it does make a LOT of difference, especially when fighting infantry-heavy FedCom RCTs. The thing is, with the exception of the APG, almost none of the other advanced tech Clan weapon are game-changers.
ATMs? The rules are cumbersome to use, and requiring three tons of ammunition for all three types of missiles hurts; plus, even with the integral Artemis IV, they have smaller tubes than Clan LRMs and generally weigh as more if not more. Only ER munitions match or exceed LRM range, and they do 1 point of damage per missile. In close, Streak SRMs are far more efficient, even though HE munitions can really mess up someone's day. And SRMs are better at crit seeking, since standard (2 point warheads) and HE (3 point warheads) have their damage divided into 5-point groups (idiotic rule, but it is there).
For example, the ATM-12 weighs 7 tons; with ammo that means 10 tons in practice (for 15 shots). For that same 10 ten tons, you can get an LRM-15 with Artemis IV and two tons of ammo (6.5 tons) and a Streak SRM-4 with one ton of ammo (3 tons), giving you 16 shots and 25 shots. Nineteen tubes versus 12, with a lot more endurance and the same heat and one less critical space, and still save a half-ton in weight. Or you could get an LRM-20 with Artemis IV and four tons of ammunition, and STILL come out ahead in everything but range for those five shots with ER munitions.
Heavy Lasers? Range of IS Lasers, a penalty to hit, and tremendous heat? Please. I hate these things because they seem useful. They aren't. If I were a Clan Bloodnamed Officer, and I met the Scientist who invented them, I'd kill him.
HAGs? Clan LRMs do it better in everything but range and potential ammo explosions (for multi-ton ammo bins; if you have just one or two tons of LRM ammo, it is a wash). Still HAGs aren't all bad, they are good solid weapons that can deliver a LOT of scatter damage down-range.
Micro Lasers? Please, these are ProtoMech weapons, not something you put on OmniMechs.
Plasma Cannons? Great for killing infanry and vehicles; just about useless (due to heat limits for externally applied heat) vs. 'Mechs. They have a short range, use ammo, and inflict ZERO damage agains 'Mechs. Want to fry infanry and vehicles and 'Mechs? Load a ton of Inferno SRMs and a ton of regular SRMs. And you've got a better weapon.
Really, the APG is the only new Clan weapon introduced that really changes the battlefield of 3050 if you move it forward. Everything else? It can already be done with existing weapons.
Now, if you want to make Ferro-Lamellar Armor standard in 3050, that's a different kettle of fish!
MA