Well, the cat is dead. 
I purchased a MSI Aegis RS gaming PC with an i7-12700K and RTX 3070 Ti and 16GB of DDR5. It runs MSFS very well indeed at my monitor’s native 1440p resolution, 100% scaling, global setting of “Ultra” and no additional adjustments, safe BIOS settings (no overclocking needed or registry hacks which were goals).
Among other things, my justification for going back to a PC included being able to have access to the planes (payware as well as freeware), repaints and other community offerings, being able to have “guns” visible on the historic aircraft that had them (dumb Marketplace policy) and being able to load FSX again for planes that haven’t made it to MSFS like the A2A offerings which are still pretty great.
For comparison to the Series X, it does look a little nicer on the PC with Ultra. I think the reasons include native scale rendering, further draw distances and a bit better anti-aliasing. Even the Series S looks great and the Series X has the further draw distances and details so that alone doesn’t justify what worked out to be a 4 fold cost (on sale even) over the Series X.
It runs smoother with this PC (which I’m also pushing harder than the Series X) including around airports but it DOES have the occasional brief stutter. I’m convinced these are due to either a large number of simultaneous AI spawns or delays in fetching data from the servers. So, another goal was to feel like I got an upgrade in terms of visual quality and performance and I believe I’ve succeeded.
In terms of the original subject line… the Series X absolutely can run MSFS well but it would do that much better if MS/Asobo added the ability to run at native 1440p and offer a few choices regarding OLOD and TLOD to dial in that perfect experience. The Series X is not capable of the default PC “Ultra” settings but it’s darn close. Now that I’ve seen both I see how people say the X sits between the PC “High” and “Ultra” settings. On the PC, “High” looks pretty darn good too and would be probably perfect for a number of less expensive PC options out there. If the Series X dialed the settings back to just “High” (or gave the end user the option) and allowed the choice of native 1080p and 1440p then I suspect it would meet most people’s needs.
If you have a Series X and are wondering about switching to a PC, I’d say proceed with caution. If your only reason is because of a little more stutters over the Series S then I’d say just wait for MS to continue to optimize it further. The expense to get to the level that will exceed the Series X on a PC hardware is huge. If you have other games or other flight simming reasons then the switch might be justifiable.
If you’re just getting into MSFS and don’t have a console yet then I’d say buy a Series S for now. It DOES run the sim more smoothly but at the expense of smaller drawing distance and slightly lower resolution ~ but don’t let that deter you because it does look great, will run all of the aircraft and scenery available through the Marketplace and the entry price can’t be beat.
One other surprise, and tip for Xbox users, is even on “Ultra” the default setting for AI traffic (all types except Fauna) is 50%! The Xbox defaults to 100% for those if I remember correctly. AI traffic can cause stutters so dial your settings back to 50% and it should help a little. It’s one of the few things we CAN tune on the Xbox.