Sure, but if you run every 7 minutes all day soon you are annoyingly offset from other buses. A 7 minute average wait is normally less than 4 minutes, and so acceptable. However if you happen to be transferring to a low frequency bus it can be a 8-10 minute wait every time as you can't trust the one arriving sooner will allow time to make the transfer.

All good transit systems are based off of transfers, and 7 is not a nice number for transfers. A 5 minute wait is okay, but 7 starts to get annoying. 7 doesn't work with a clockface schedule. There is no city in the world so uniformly dense/rich that they don't have some lower frequency routes that need to run a clockface schedule on. With 7 minute frequency you can never learn what what time you need to be at the stop to make the transfer, which destroys the whole point of a clock face schedule.

If you are lucky enough that you never need to transfer, then 7 minutes is frequent enough. However it doesn't play well with the rest of the system.