The lighting system shouldn't tank your FPS I think a redone lighting system would be very beneficial for the game to improve FPS
Well... I hate to be the bearer of bad news, but the lighting engine was pretty much just redone (I believe) along with the render engine as evidenced by everything still making the switch to PBR.
Honestly i think its a wonder my PC still can run Beamng with decent FPS being a i5 2500k, 8gb ram, 1050ti. If the lighting tanks your fps then i think its on your end. Ideally id go i9, 32gb ram, and a rtx 30XX-40XX but my pc game pockets arent that deep lol