I wouldn't say this is a matter of how many gates he can use, the fact his that Guy is all Taijutsu and Danzo has 10 Izanagi to use, which makes it relatively easy for him to use his juinjutsu on him. KA isn't restricted either so, KA ftw.
Imo Danzo low-mid by the above mentioned reasons.
I always find it funny how people think Danzo is that good he has a small number of moves he is older and he has to unlock his arm to use izigani.
If he arm isn't already unlocked Danzo isn't even low Kage level.
Without fu and the other guy forgot his name to be diversions he wouldn't have been able to unlock his arm.
Guy is way fast and relentless so I doubt he would have time to unlock that arm hence making izigani useless if he can't open that arm.