Ahem lol...I'm not questioning you...or me...I have FS9 running under Win 10 as well. (thumbs up emoji)
I've done all of 3 or 4 flights in Win 10 but already found issues. There are some graphical issues with gauges. This may be my system but it's exactly the type of thing that happens trying to run old stuff on Win 10. May be my graphics card drivers, may be my hardware, regardless, may or may not be possible to find a fix.
Then there is FS Recorder, a very popular add-on. Have not found it possible to have it's control window open with FS in full screen mode. Again, have not done a great deal to find a fix yet, be interested to read anyone who can do this on Win 10.
Then there are a couple of potential issues with the iFly 737 which I need to explore further before commenting.
These things are a typical example of what it is like trying to run old software on Win 10. Just about every old program has problems and you then need to find fixes. Some software has fixes, others doesn't. It's an incredibly frustrating OS to run for old software.
You'll never run FS as problem free on Win 10 as you could on Win 7. If anyone suggests they can, they simply haven't used the problem add-ons yet.
I'm not stuck to any system. I have Win 10, Win 7 and Win XP. Each PC capable of running FS9. I'm going to use the best choice for FS9 but it certainly is not Win 10.