The way that whole giving MiGs to Ukraine affair went tells me it wouldn't matter whether Ukrainian pilots could have been trained to fly western jets in the years prior, cause the west would be just as reluctant to supply Ukraine with those too.
If training were the only issue at hand there, those old MiGs countries such as Poland have in stockpiles would already be in Ukrainian hands making sorties against the Russians, but the initial transfer didn't even happen. There's a reason for why Poland wanted to give them to the US first as a middleman for transferring to Ukraine.