The theoretical ROF is usually no indicator on the actual combat effectiveness of a weapon.
The BAR and the FG42 are extremly different pieces of kit and are hardly comparable. Depending on situation one is better than the other.
The BARs ROF is significantly lower than that of the FG42. The A2 version of the BAR wich is the one widely used during WW2 cycles with less than 500 RPM. Combined with its high weight of allmost 9 kg it made the gun very controllabe in automatic fire. The BAR as such also is very accurate since its more of a full auto rifle than an LMG.
I dunno why people always want to get so technical in these discussions. These arguments about guns is an age old debate, that's my entire point dude. Nobody cares if the BAR is better than the FG42 or if the FG42 is better irl. And btw, you're talking about the FG42-1 that has a 900 RPM. The FG42-2 has only about 600 RPM. BARS shot at around 400~650 RPM depending on the selectable firing mode.
In this game, falschimjager are seen more common with the FG42 than rifles with BARs. Does that make any sense? IRL the BAR was the most common weapon on the battlefield and the FG42 was nearly non-existent. Historically accurate? No. I dunno how people say the FG42 was more superior when it was BARELY even produced and used. It's like saying the Super Pershing was the best tank of WW2 except only 1 was EVER used.
Anyway, this game sucks balls. Doesn't matter if you want BARS/bazooka's to be more accurate or cheaper. The Relic balance team is ran by 1 dumb ass scrub that barely knows how to play the game and wants the game balanced his way. That's all it amounts to. I mean, who the hell asked for a kubel buff and half these changes? That's the problem with relic. They come out with a huge stupid change every time when top players ask for like 3 units to be changed.