As long as the game is DX11, we will deal with issues until MSFS 2030. The main core is already cramped with stuff. Right now they are taking stuff out to give room to new stuff, or trying to balance what should stay and what should go. Who was here since day one knows what I’m talking about.
Even if they introduce DX12, it will only make a difference if they rewrite the code to parallelism to use multiple main threads, which I don’t think will happen, since the code was resumed from the FX 2006. They would have to practically create a new game for DX12 (and they coded this one for years). My bet is that we are going to have performance issues until the next iteration of MSFS, unless they could share some of the load with a second main core or something.
What I agree is that a 5900X is a waste of money even for current DX12 games. Unless you render and edit on a pro / Youtuber level, the 5800X is more than enough.