Yea, I'm calling bullshit. Lighting has never impacted game balance this critically. Marines at the current moment are able to chase down lurkers and runners easily in areas where there are no flares just using their armor shoulder lamps. Nor does the current lighting mechanics allow castes to sneak up on marines since there is sufficient light to see them from 5-6 tiles away.
With CM hitting +200 players regularly lighting needs to be looked at. 150 marines are raycasting on ~60 tiles each. That's almost 1,000 heavy calculations per tick that is updated constantly just to have a cosmetic feature that is window dressing.
I'd recommend scrapping lighting for a few rounds and see how well it fixes the lag. My hunch is that lag will vanish and gameplay will be normal.