Its noticeable that the shift-rpm is used as the point as which engine damage accrues and this just does not seem right, shift point is usually the point of maximum torque and minimum rev drop between gear shifts - idelally it should be adjustable in the garage and is a riding aid. Going above this point does not necessarily mean the engine will be damaged or excessively worn.
It does not seem necessary to model general engine wear as we only run a single race/engine and its unlikely a modern engine would just wear out mid race - it might be interesting and worthwhile if engines were limited in online sessions and wear retained between qualify and race day.
More realistically it should accrue significantly at any point above the limiter (which can happen due to over aggresive shifting/bad quick shifting) or as the engine power curve moves past its peak power rpm design point, again probably quite significantly damage at this point as it is usually mechanically limited by connecting rod strength and valve bounce.