i think FSX has some major problems in it
It does not.
a) The FS series is being developed for a "market life span" of two or three years, meaning that it *has* to look good and up-to-date even at the end of its service life. So the developers have to program the according graphical elements and environment which even today's high end computers can't handle by 100%. Mine for example runs with 90% of the settings maxed and that's IMO already very good because the graphical quality made a bigger jump than it did when FS9 came out (which actually only was a polished FS8).
If I slapped a faster CPU into my PC, I'm sure I could run my FSX at the highest settings.
b) Check the tuning FAQ for some FSX tweaks.
c) Always keep your drivers updated.
d) Do a defrag.