God, I feel this. Artists can be an absolute nightmare to get on board with any marketing that isn't just "post the song and pray." Pulling teeth just to get a seven-second TikTok out of them? Been there. They want maximum reach with minimum time away from their "real work" - which, fair, but someone's gotta do the grunt work.
For marketing here, if the artist isn't already a native user or has no existing community, it's going to be brutal. Self-promo is a minefield. Best bet is finding specific communities that actually allow sharing links, and even then it's more about SEO/visibility than going viral. Painfully slow.
From an agency angle, I'd say meet the fans where they already hang out - Discords, SMS fan clubs, maybe a niche subreddit if the audience is already there. But trying to force a fan base onto a platform they're not naturally on? Not worth the budget unless you're working with a legacy act trying to tap a specific niche. Otherwise, you're just shouting into the void.