You touched on one of the bigger issues - although the Ai “logic” needs to be completely updated (and accessible which it currently isn’t), nearly every airport in the game needs Ai pathing to be corrected. This is a pretty large task. It is certainly doable, it has been done in the past with “packs” that fixed large numbers of airports. Unfortunately, this requires time and tools (some of which are still being worked on now by groups at AIG, which has recently said that MS2020 is somewhat of lower priority now because of the limited SDK).
What surprises me (no, not really), is that even “handcrafted” airports have major issues indicating that these types of issues are very low on the priority list (or perhaps, not even on the list). Here is one example: