in my time mapping so far, I have yet to find 1/7 in the songs I've worked on, and I like pretty complex music. Have come across 1/5, (actually working on a map rn that has 1/5 guitar runs in the beginning, even had to double bpm briefly to get a 1/10 kick slider) but its usually so brief that mapping it actively with bursts/streams in STD mode would just be a dick move, worse than those super spaced jumps into a super slow slider on pp maps.
quint and septuplets are just really rare outside of super polyrhythmic music like II-L makes.
definitely easier to find in other gamemodes though. Players can read rhythm changes from the distance between the objects scrolling/falling so it can be mapped actively even if it only happens one or two times in the song.