I didn't want to be biased but agreed, Mig-21 needs some help. The Gazelle could use help but I fly rotaries for fun so I don't care if its bugged.
The question about more content missions, campaigns etc. I don't know were to start. There are too many module I would like some campaigns for.
Just ran across this vid and looks interesting. Started to follow but I didn't have the P-cores button option though I have an i-9 with what looks like 15 cores. From the comments it looks like the suggestion is to split the cores, put DCS dedicated on half of them and all the other processes on the other.
Not sure how much time this really saves by time you first load up the map in the editor, but it might help with potential crashes when getting into a MP server?