If one wanted to drastically simplify scheduler, for example for some scientific application which doesn't care about preemption at all, can it be done in clean, modular way? And will be any benefit?
But the reason for drastically simplifying it would be to avoid bugs, there isn't much performance to gain compared to a well-set default one (there are plenty of settings tough). And there haven't been many bugs there. On most naive simplifications you will lose performance, not gain it.
If you are running a non-interactive system, the easiest change to make is to increase the size of the process time quantum.