well itachi has susanoo and its weapons, kabuto cant bust it open, itachi also has amaterasu, but kabuto and his perception and reflexes seems like susanoo wont touch him, and he can liquify himself, or use sound genjutsu and white rage, plus muki tensei at itachis feet, or give any source around them life, his sution counters itachis and his katons too.
he can probably shed his skin if amaterasu ever touched him, and he has karins uzumaki healing enhanced with sage mode, kimimaro bones enhanced with sage mode, so taijutsu is kinda hopeless without susanoo, chakra scalps, the other sound 5 as well and can shut off his vision, i think he dodged a susanoo arrow without even lookin while in the mouth of his snake, so i dont see susanoo catching him, he also has oral rebirth
im not a kabuto fan, but instead of us just saying "if he didnt hold back he would win" we should try and talk about how they counter eachothers abilities and stuff....i hope i dont sound biased cause i really do like itachi, but kabuto just has a lot of abilities that dont seem to require having to break open susanoo to be viable for him against it. but i would also like to hear arguments for itachi (excluding izanami of course)