Could have been, but I already checked that (I know pretty well each processes running in background, I use to search malware and virus just by reading the list, part of my job). My guess with MSFS is online dependency is heavy and also they are some fishy settings in the Sim (E.g. sometimes reducing a settings and you get lower perfs until you relaunch several times).
And to be more precise I don’t check fps, I check CPU, GPU, RAM and storage % usage. I can have same fps but better GPU headroom for example. It’s mainly those usage tests which are inconsistant in MSFS (mainly, good things happen sometimes 
)…
Benchmarks in other games are pretty consistant on my machine (Cyberpunk 2077, Horizon Zero Dawn, Assassin’s Creed games, etc. ) so I use them.