He starts with gigantic suiton, but not giant enough to overwhelm the opponent. For that, he needs Bijuu level chakra
Says who? Part1 Kakashi was considered a threat for Kisame according to Itachi, who even stated he won't get away scot-free if he was challenging him. Kisame himself noticed(surprised) that part1 Kakashi was strong enough to even hold his own against Itachi.
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, Konoha, Suna and other kages disagree(they consider him as worth Kage level ninja) and i'd take their words as characters of Kishi's manga over your opinion