I'm not prepared to go into a TBM vs (insert add on here) debate and which is better/more complex/etc...
There is a lot going on under the hood of the TBM, and although I do see the spikes in your graph, you haven't mentioned the variation in fps. I just tested this myself, and the spikes in my graph represent a variance of no more than 2fps on an average of 40fps on X-Plane 11.41.
This variation is more than acceptable for me. Why are the graphs smoother in the 172 and FF A320? I have no idea. I don't know how the A320 is coded, and it's likely I never will. I do know what the TBM has that the A320 doesn't, and this may have an effect on the fps. But again, I don't know.
Of course, we COULD take some features out, and it would reduce the stuttering dramatically, but that would defeat the purpose of what we're trying to accomplish with the TBM.