Interestingly the old saying, “If it ain’t broke, don’t fix it.”, comes to mind.
There is very little that needed to be changed from FSX to be able to provide rudimentary ATC. For generic use this system works quite well when the information provided to it is complete.
As long as the flightplan contains all the relevant information, the ATC system is nearly flawless in getting you to your approach. Too many FPs that are created with the world map are simply “fly direct via GPS to XXXX”. The default ATC is going to have an issue getting you from a direct GPS track terminating on an airport into a proper waypoint to transition into the correct STAR and Transition so that it can get you to the IAF. Your lack of planning is not ATCs problem. Combine that with altitude restrictions and enroute MDAs and you have a recipe for granite soup.
There have been numerous attempts to release aftermarket ATC adds. None have worked any better than the default. Some handled multiple aircraft better, but only when used with aftermarket AI aircraft adds, some handled vectors better, but let’s be honest, the ONLY add-on that truly made an improvement was virtual ATC using humans.
There is a reason the world of aviation has never implemented AI ATC in the real world. If we could have realistic, accurate AI ATC implemented in a $XXX simulator, I am pretty sure that would be groundbreaking.
The reason many are “OK” with the current ATC is because, for the most part, it works.