To be fair later versions of the Mig-29s are very capable platforms. The key is to know when these Fulcrums were produced and what designator they carry. Mid-80s Fulcrums were roughly on par with F-18s of that era (though F-18s have been significantly advanced over the decades to make them better than any version of the 29). 29s are still produced I believe, and later versions are pretty capable. Not against top line US aircraft, but they would be fine against most of the stuff the Russians have (this again assumes these Polish planes aren't 80's vintage issue).
Also, Ukranian pilots and crews are used to Soviet fighters. They don't know how to fly or fix NATO platforms, so it isn't as easy as saying give them some F-16s! They couldn't fix them. Or fly them.