FWIW - I had one in a standard 30g for over 7 years (I don't know why it died) prior to that a had a different cherub angel in the same tank for about 1.5 years (that one succombed to a hitch hiking mantis shrimp)
I think a key is the tank mates. Most of the time the only other fish were an ocelaris clown and flame hawk. So no other algae eaters and all about the level of assertiveness - no one really agressive, and no shrinking violets. My cherubs ate anything - flakes, pellets, etc.
Just my experience - every fish is different.