My lack of planning. I guess that’s a fair assumption.
Maybe blame Simbrief instead or even better, the airlines. Because more often than not I just copy and paste a route I get on FlightAware to replicate a certain flight. I used PFPX in the past as well. I think I am able to properly plan a flight, but maybe you are right and the issue lies with me.
You are making good points, because altitude restrictions and constraints are also often wrong in the nav data, from what little I can tell by flying the FBW A320NX and comparing it to the charts. If you are using a Navigraph subscription for nav data you might not notice that of course.
At or above constraints sometimes become at or below constraints in the sim. I could very well imagine that this interferes with the ATC in some way during an approach. That said, the ATC also struggles with accurate SID/STARs.
My experience with the sim is, that I get assigned the wrong approach transition sometimes, no matter what is in the flight plan. It mostly works, but not every time.
I think most aftermarket ATC addons were restricted by limited budget and market prospects and also the limits of the SDK. But we are talking about Microsoft/Asobo here, not a single developer working from their basement.
I am “OK” too with the ATC, but I still wished for something better and think that would be reasonable. Only an opinion, I know.