well, I readed naruto from the beginning but my mind if foggy (whoops pun xD), I'm going mostly by Zabuza's profile and what I can recall, Zabuza is listed as supersonic+, I assume this goes by combat/reflex speed, and possibly to his movement as well, making Stain's higher, even if his movement speed is only subsonic, Todoroki and co probably arent stronger or as experienced as zabuza (tought their stats on their pages are superior) the relevancy here is that Zabuza's large scale jutsu require at least a brief period of "prep" time (how to forget that long sequence of hand seals for the water dragon bullet jutsu). this brings in the next point, its clearly stated as a weakness that zabuza requires large amounts of water for certain techniques, this goes pretty obvious for the large scale ones, only adding more time he needs to spend creating it from his own chakra.
mentioning again the setting, gotham city at night, its not like in the middle of the city there are the required large amounts of water, unless we go somewhere like the docks,cant say much about the mist, its a good advantage.
worth also mentioning, despite zabuza's higher durability, Stain's speed and quirk can nuliffy it, its not like having 8-B durability makes you inmune to being grazed by knives, and Stain has already hurted enemies with far greater durability, tought probably due the effect's of his quirk (He paralyzed and then harmed, probably killed a noumu, Said noumu resisted Endeavor's attack, who's ranked 8-A)
Lastly about the diverse skillset, and going again by zabuza's profile and your suggestion, he'd have the 3 basic genin jutsu (cloning, transformation and substitution, 2 of which are neutrallized by Stains speed), aside from that, the rest is just "more ways of manipulating water", which is not far from extended quirk usage in BNHA, specially considering most ninja abandon basic genin jutsu and focus on specialized jutsu of their own or their clans. the "zero experienced against multiple powers" point is nullified in the fact that both zabuza and Stain have fought and killed several oponents with different powers, its noticeable from zabuza's background, and we have a number on how many pro heroes Stain has maimed.
Stain only needs a gracing with any blade, and the combat is done.