Hi ,
(According to my view)
For Mobile network I don't think it's going to make any difference , as it's module of android system integrated with hardware so optimization or not it will work the same .
System UI have nothing to do with gaming , but yes disabling optimization for UI ( May or may not ) prevent apps from shutting down at background (I know it mostly depends on R.A.M management but this is alternative way to shutdown app in background to save power ) .
Android OS or System is just a middle man which interprete between games , kernel and hardware .
Performance of games are dependent on storage speed ( Random RW Speed ) , Governor Settings , kernal and hardware .
Coming to the point optimization enable or disable real doesn't matter when it comes to Android os or System either ways it's kernel who will bypass any restriction made by software and performance as it is meant to be .