This is tricky because almost any situation is going to have qualifiers
For example teen jean kept galactus at bay. But people could say “it’s only because she had the Phoenix nearby to siphon from.”
She also held her own against ultimate dr. doom. That was a pretty formidable foe without any qualifiers.
I honestly think there aren’t many foes jean couldnt beat if she’s giving it her all. Aside from regressive characterization and writing, the only thing thag usually holds jean back is her morality / trepidation