How much more is realistically fixable

[Trumper]

This is meant as a genuine question not to start a flame war.
I wondered just how much more of the sim is fixable, able to be repaired /tweaked by the developers.
Does there come a point when everything has been looked at and optimised and short of starting the whole lot again it reaches the best it can get.
I wondered how far down the line they are now.
Patches are patches and seem to be ok for some and not for other users so where is the deciding line?