Feats aren't all there is to versus threads. The manga doesn't hand everything to us like babies. Some things in the manga could be logically concluded once we put two and two together and use a little bit of common sense.
If everyone proceeded the way you do, Kakashis Genjutsu he used back in part 1 on Sakura during the bell test should allow him to solo anyone in the series who has no feats of breaking Genjutsu, right?
Actually, in this case in particular, we can infer the results for two reasons:
A. Kisame already failed to break free of a way weaker genjutsu by a way weaker genjutsu user (Kurenai)
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B. Kisame's genjutsu stats are pitiful at best
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While Orochimaru, who got a solid 5
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Did notanaged to before he got his hand chopped off. So no, its not baseless assumption.