You seem to be ignoring the effect of Windows Updates to the equation (interesting none of you are talking about that), and none of you mention AV, or other junk running in the background.
This is on top of the fact that the later updates of MSFS are slower/worse than earlier builds (I noticed a significant drop around SU10 that has never been recovered).
None of my OS or drivers have been updated over the entire time I have been running MSFS, so the only change was MSFS.
Frame gen is a con, with the GPU creating fake frames that games have zero idea about. Sure, the GPU is kicking out 5000 FPS, but MSFS is still running at 20 FPS internally, including physics. All you did was add lag.
Stutters can rarely be fixed by hardware. They are software induced, so your only option is to remove it all and put it back one-by-one to find the culprit.
If re-installing Windows fixes your issue, you clearly had a bad driver/update that you were unaware of. The latest is not the greatest.
SMT is the AMD equivalent of HT on Intel processors, and can have significant negative impact on performance. As was mentioned further up, it divides physical cores into logical cores, so if you have 10 actual cores, SMT makes it 20 logical, and when a core goes idle for the remainder of its time slice, Windows will try to schedule something else into the free time at the end of the slice, but OFTEN gets this wrong, screws up, and whatever was assigned to the remaining time exceeds the time available, and delays the processing of the original task that is assigned to that core. Instead of making things faster, it slows things down, and causes more context switching than necessary which adds its own overhead. It’s a rubbish system in practice, and best disabled on every CPU whether AMD or Intel.
MSFS is also dependent on the internet, so don’t under-estimate what effect this can have on the smoothness of the sim. This is also down to your motherboard and bus design as to how much IO affects memory access, as cheaper motherboards lack buses/lanes/features for incresing performance. This manifests itself as stutters during disk IO, etc., and in completely unavoidable in some cases. The ONLY option is buy top-end motherboards and chipsets, and forget everything else.
Obsessing over CPU utilization is also pointless, as you don’t know precisely what the software is doing at any moment. If you think all cores should be maxed out at 100% for best performance (same for GPU) then you have zero idea about how modern computers work. MSFS is not some massively-parallel compute platform. It’s a game, with a game loop and a bunch of stuff that needs to be synchronized. That immediately requires something to be idle at some point while waiting on results from something else that can’t be calculated in parallel. This is also why no simulator can ever use “all teh cores!11!111!!” that people think it should, because it simply can’t be parallelized to do so.
More important than absolute FPS, is the 1% and 0.1% lows. This tells far more about a processor/bus architecture than max FPS. Here, Intel is better as it generally has higher lows vs. AMD in the same situation.
Where AMD excels is it has more cache per core, so less cache thrashing than Intel, and this is why for certain loads AMD is far better. The question is whether a program has been suitably optimized to maximize this cache usage. Software design has as much to do with this as amount of cache available. It matters not how much cache you have, if program data exceeds the cache size. This is what REAL optimization is about. This ignores specific instructions on AMD vs. Intel, and how well they perform at the instruction level relative to each other. This is why certain games/benchmarks prefer certain processors.
As you can see, performance is a whole lot more complex than simply whether 10% or 50% of a core is being used. None of this matters when the software is fundamentally broken in some way due to a junk update that broke something (we see this very often with Windows, where many patches are fixing the screw-ups of earlier patches).