if that's the majority of the issues you see, I'd probably just try turning off the sunshafts with
r_sunshafts = 0
in a user.cfg ....
the reason they run like ****, is because they always have done so, and its specific to the engine version of the fork we are stuck with .... the time of day system doesn't get prepared before its put into action, which tends to cause a pause if its started, or stopped ... and I don't think anything PGI could do would really affect the flaw in the early version of cryengine ... in later versions, they changed the methods and it probably runs smoother ... but were never going to get that into MWO, because they cant update the underlying version of cryengine, without re-doing everything from scratch .... the lesson being, when you fork code, make sure what you write is modular enough that it can be adapted to later versions ... otherwise your code is stuck in a bad time loop from 2013, as we are ... theres things you can do to improve the inner workings of the lighting systems, but there isn't much point, because it cant be fixed on the client side ....
then theres scratches, whats a scratch ? its the bit that makes a mech shake when you receive an impact .... for reasons that not even god herself could explain, they went with a method that includes the sun in calculations .... because the sun totally affects the screen shake ... just another example of a lack of forethought .... and the majority of lighting stuff isn't handed off to the GPU, that would be too taxing for 2013 hardware, its all done on the CPU, and on the assumption your going to be using a lower resolution than 1080p ....
maybe things will be better in MW5 ... but seeing as they've only talked about a single player campaign, its not really going to affect or help us at all ... I predict that 'eventually' they will port MWO into the unreal engine ( like in another 2-3 YEARS ), and its going to be as bad a mess as MWO is atm, because they don't believe in foreward thinking .... just knee jerk reactions and mech packs ....
still waiting for $1000 USD platinum mechs to become a thing, when everyone gets jack of paying them for no improvements, and they need to raise capital