agree, with the exception that he can feesibly beat even EMS users with 7th gate. We have seen ameterasu latch onto chakra shells and burn through them, but it is unknown, and seems unlikely that it could latch onto a powerful gust of wind like gai would be able to produce punching the air toward ameterasu. If i recall correctly, gai also once either used or suggested with plenty of confidence that he could contend with most any uchiha by looking at his feet the whole time during a fight, so assuming that wasn't just him being cocky, he can thus negate any controlling genjutsu. Anything shy of madaras perfect susoono could very likely be shattered by 7th gate gai because it is arguable that while in 7th gate he is, if not stronger than raikage, most certainly stronger than tsunade (only during that short time frame) and we have seen her crack through an imperfect susoono. Honestly the only people in general i see him losing to handily is an ET summon simply because with overall infinite chakra, and perpetual regeneration, gai has no way to truly defeat an ET since i dont recall ever seeing him use a sealing tech (correct me if im mistaken?). Now for personal fights as opposed to general. Sasuke would not hold a flame to gai in taijutsu, nor would his general ninjutsu techs have any effect, so i see him getting frustrated and start spamming ameterasu which wouldn't blind him now but would still wear him out using it, leaving him dead on his feet unless he covered the entire battle field with it. Itachi, while i feel more cunning, wouldn't fare much better. In his human form, he was sickly so that puts him at a big disadvantage, but for fairness lets assume he was healthy. Even when healthy itachi was never known for large chakra reserves so he would have to use his techs sparingly, and assuming gai could fight without looking above his feet, it would also render itachi's sharingan more or less useless since he only attained MS while alive meaning a few ameterasu and he loses his eye for the battle, and a much smaller window to use susoono, also noting that gai should be able to dodge the sword, and the yata mirror should have little effect since gai uses mainly taijutsu (no chakra of any kind to counter). Itachi was also not known for having much stamina even when healthy, so his only hope would be a quick finish with taijutsu but in my opinion, gai is one of the few who could outperform itachi in taijutsu technique, fully becoming the ultimate bad matchup for living healthy itachi.
