With artists moving to other sites, I think one important thing to keep in mind is the difference in the intentions behind a site’s social functionality.
When people voice concerns over twitter, people suggest things like Pixiv and Newgrounds.
Sites like Twitter, Facebook, Mastodon, and tumblr are what I consider social-media focused sites. These are sites that let you share other peoples’ work as well as your own, and focus more on moments. They have photosets and primarily focus on your dashboard. It can be much harder to find content in the backlog of stuff, but you also have way more interaction with followers. They also allow non-artists to do things such as content aggregate, which if done properly (with the built in sharing functions like retweets), help artists out.
Newgrounds, Pixiv, Deviantart, Furaffinity, etc. are gallery / content-focused instead. These are sites that focus more on your presenting pieces, archiving them, and focus less on interaction and more on the content. For these sites you usually don’t have a dashboard, or it’s not a focus, you instead have a notifications page. It’s very easy to check out prior works, but that’s all you can do aside from comment or review things–your sharing options otherwise are limited. Users who do not produce content are more limited in what they can do on these sites, and mostly just curate personal favorites or write reviews.
Tumblr had a caveat with tags and archives that let you run it as a gallery as well, which was very useful, even if it was more social-focused. Overall tumblr could function more how you wanted to, and kinda got the best of both worlds, which is why it’s a shame this is all happening.
Comparing Newgrounds to Twitter is moot because Newgrounds isn’t even in the same race as Twitter.
So the question shouldn’t be “should I get a Newgrounds account now that Tumblr is dying?” Because you should probably get one anyway, even if Tumblr were fine.
Or whatever gallery platform you want regardless. Get one in addition to whatever social media platform you end up on–choose one social and one gallery focused platform. Gallery sites are not as high maintenance as social ones as they’re not as impulsive, and are much more stable places for people to find you if something happens again.
But this is also why Twitter is the popular choice–because, in reality, it doesn’t have much competition without Tumblr, since most alternatives aren’t even social-focused. (hence why I’m eager to see how Pillowfort turns out.)