Every flaw that the Perseus has is laid out right in its FM/TRO entry (notably, the crowded internals and all the resulting effects of that).
The B variant is my personal favorite, and I totally get the criticisms of it. The ammo issue is a function of the original AMS ammo consumption rules, so if CGL wants to retcon that second ton of AMS ammo into Gauss ammo I'm not going to play dentist with that particular horse. That being said, we're all so used to looking at the big 15-point slaps of that weapon and thinking of it as the primary weapon of the unit it's mounted on.
That paradigm doesn't apply to the Perseus. That Gauss is a weapon of opportunity that you can slip into your firing order in turns where you have good to-hit numbers. The trio of large lasers are the actual primary hole-punchers for the B. The ISLPL likewise is not a popular weapon around here in my experience, but it's extremely common in Invasion-era Marik units. The ERLL is a token long-range engagement weapon while closing, but the twin pulses are the weapons you need to be considering when looking at movement & range bands. It's a brawler. Once you're in good ranges for the LPL, you should have decent numbers for the Gauss so you can start tossing slugs out without worrying about wasting ammunition. It's also the only config without guns in the legs, so yes! Grab the enemy by the belt buckle, give them some pulse lasers, and then sweep the leg.