I think it would be good for the game to set a limit of submissions per artist to 10. Technically, this must be precise: the name of the act, artist, band , project, must be exactly the same to be forbidden more than 10.
Examples: John Lennon and the Beatles are two different acts. But also any act prominently fronted by an artist under a different name can be considered different - which would be technically the only way for mischievous players to contourn the rule. But at least there would be a limit.
Other examples: Prince and Prince and the Revolution: different acts. Neil Young and Neil Young & Crazy Horse: different acts. Teddy Wilson & his Orchestra and Billie Holiday: two different acts.
This rule would on the other hand forbid the submissions of any act which has been submitted already more than ten times under the same name - for example: Madonna, Björk, Lana Del Rey.
Technically for the manager or any player willing to help, this forces to verify the exact name of the act submitted (artist, band, etc). It's easy, but you can't trust YouTube only for that.
Also maybe it's a work that should be done already for the used list, which could be time consuming given how long this used list is already.
Of course, a poll must be sugggested to all the participants of the game to apply this rule. It can only be applied if it gets a major agreement.
Feel free to reformulate my suggestion for the poll as my english isn't perfect. Also feel free to only submit this poll if you agree with this suggestion in the first place. I'm not a regular player anymore anyway.
Have a nice day