Violetta (G3) vs Masaji Kato (SH2) - This is actually moderately close. Violetta's damage was only okay IIRC, pre useless-in-this-fight debuffs? Meaning she might not OHKO part of the Regalia, meaning Kato might live to unleash his super-combo on Violetta. Fight turns on this. Leaning Violetta but general Kato HP respect makes this interesting.
Guv (DQ8) vs Ultimecia (FF8) - No Call Team, No Dragon Soul, so close fight. This is entirely about how fast Guv gets doubles and if his MP holds out. HealAll doesn't cost much MP, bug Gigagash does cost some, and Gigagash is... what... 5HKOing the final form here or something? (Earlier forms probably get OHKOed and 2HKOed a bunch, so not a big deal). Ulti is slowish but I dunno if she's giving up that many doubles to Guv before his MP is gone.
Heavy
Galcian (SoA) vs Peppita Rosetti (SO3)
Meliadoul Tingel (FFT) vs Neclord (S2) - I really want to vote Meliadoul on "lol S2 bosses" logic.
Odin (VP2) vs Albert Simon (SH1) - Simon's physical is inconsistent, as I'd hold bosses to not being able to spam 3-hit versions. And I think it's his best damage here? Anyway, Odin has ~1.1xPCHP to me, Simon has ~2.5x PCHP. Simon should 3HKO, so it goes something like Simon / Odin / Simon / Odin (Spiritual Lancer) / Simon (win). Yeesh, much as I like to hype Odin myself, I don't think he wins this one; SL + other damage should be about 1.5x PCHP worth of damage, so he can plausibly win if you scale Simon's HP harshly, but not enough for most interps I imagine.
Middle and Light are Suiko / obscure stuff overload.