Mastodon: No. It's a very shitty alternative to Twitter where the quality depends wholly on the instance you join. The discoverability of federated content is so bad that if you go into that tab, you just see nothing but porn.
Lemmy: Possibly... It feels like a far less astroturfed alternative to Reddit.
Log into any Mastodon instance that hasn't defederated from Mastdn.social, Mastodon.social or Yandere CC and click the Federated timeline button. Prepare to have your feed swarmed with bots reposting porn. The last one is particularly concerning because it allows content that wouldn't even be allowed on LemmyNSFW...
...If you're joining a site called Yandere, aren't you going in with some expectations of sexual content...? Or am I off-base in my understanding of yandere? I know it doesn't necessarily have to involve sex fwiw, however in my experience a decent amount of Japanese manga/anime online that leans romantic also goes straight to lust town, especially if fans have any say.
I joined VeraciousNetwork, a gaming instance running on Mastodon.
The problem is that if you check your federated feed (which is a damn necessity on a smaller instance), you see content from all the instances that haven't been defederated from your home instance. The reason I haven't used Mastodon since is because my feed was filled with porn and hentai from these three instances.
Worse, I saw the 'loli' hashtag on one of the tweets and noped the fuck outta there.
Damn, yeah, that's enough of a bad first impression (mainly the "loli" shit) that I'd be put off from it too. I'd misread/understood your post at first (as you having joined the named instances vs. one federated with them), so my bad there!
That's one of the misfires of folks trying to tell people to join any instance when suggesting Mastodon/Lemmy. The instances do matter, as you rapidly found out, since the admins/mods determine which other instances you may have the misfortune of seeing posts from.
I managed to avoid a similar, "uh fuck i'm out" experience by doing a little more digging on the first Mastodon instance I joined, but I recognize that really shouldn't be expected of everyone.