Definitely not the best duel player, however I play duel enough to make a relatively accurate tier list. I try not to repeat myself throughout the tiers, however when it comes to finding the difference between something such as an S and S- tier god, they are basically the same thing, with one just being slightly stronger. Also it's quite difficult to call a god "bad", because most gods can do well in duel, however considering the game mode is ranked, most people will want to play higher tier gods (S, S+, SS) making what seems to be an average,A tier god, much worse than it may seem.
Gods that should always be banned and should win 100% of the time regardless of skill, unless it's a mirror match. (No gods here because there just simply isn't a god that good in duel right now, you could argue gods such as Bakasura, however he can even have bad matchups and can lose game.)
Gods that are incredibly powerful in duel and should always be banned unless being played. Unlike SS, they can still lose if the person playing them is not very good, or if their opponent is better.
Highly powerful gods. Banned relatively often however not as much as S+ and SS gods. Easily can beat S+ if a good player is playing the god.
Slightly worse than S, still powerful gods however are usually not banned. Can beat higher tier gods, however usually is unlikely unless a skilled player is playing.
Above average gods, these gods are almost never banned and should't beat S+ or SS gods, A+ gods are usually comfort picks from the player. (Gods that a specific player can perform well with, with this information you could say that a A+ god could beat an S+ or SS, but it's still unlikely.)
Average gods, nor good or bad however considering most people pick higher tier gods, A tier gods will have a rough time.
Slightly below average, can still win if a player is good enough however shouldn't beat S or above tier gods.
Gods that should not win unless the player is much more skilled than the enemy. These tiers and below will consist mainly of guardians and some mages, for those are the gods that struggle the most in duel.
Similar to B tier, however more emphasis on needing a high amount of skill.
Gods that should never win if the opponent is playing anything above A tier, incredibly higher skilled players might be able to beat some enemies, however this will almost never happen.