When I was working in Moscow I visited the MiG plants , what I learned. As ratty as the Migs are said to be, they can do an engine swap in less than 8 hours, in the field. Designed to be supported and operated in the field, unlike western aircraft, a big, big plus.
More, but my money goes on “ Vlad’s rusty old equipment “, just a comment from one who has been there.I will further “ forecast”, as with the Ukie failed offensive- we will see smoldering F-16’s AND M1’s ( IF they ever arrive in theatre).