Technically, meltagun CAN be described as they did in v. 2.0. In essence, it is a gun that fires a burst of highly concentrated and super-heated plasma, which at close range has so high armour penetration rate that it effectively ignores armour completely, but at mid and long range dissipates to just a cloud of your regular plasma. Highly arguable point of view (and personally I prefer the old outlook on meltaguns), but it could be done in this way as well.
The same goes for sniper rifle - yes, it looks (in my opinion as well) silly that a sniper has to spend two rounds to actually make a called shot... but then again, consider how a sniper operates. The sniper rifle is a weapon of precision, but it is a nightmare to aim through a sniper scope at speed (especially if it has a view magnifier). A master sniper might pull that trick perhaps, but your average Man-With-The-Gun will have to take his time to land a shot.
The main problem with the new weapon / armour stats, IMHO, is not that they're broken or unbalanced - they just don't conform the established / historic / fluff / whatever view of how they are expected to work AND they contradict the previous stats we're all used to. Simply put, they feel wrong compared to previous material, tabletop or roleplay.
One (not ideal) solution I see here is for us to stick to old equipment stats as they're shown in OW and BC. Granted, we'll have to attach action points to old weapon profiles, but that's no great challenge I guess