I think a kinda neat and apt representation of the sort of thing I do with my legacy characters is what the Archer series has been doing the past few seasons. They take the same core characters and tweak them to fit into fun new settings. It's a lot of fun to figure out how you could fit a character into an entirely new setting! The characters are the same people at their core but the setting specific parts of them have changed. It's also a really effective writing exercise and I quite enjoy it. Like, who wouldn't enjoy the challenge of turning a velociraptor trainer from a Jurassic World RP into the alpha of a pack of lycans?

I could understand why some people might not like that or it just doesn't work for them, but I think it's kind of ridiculous to act like there's an objective 'right' or 'wrong' way to create, play, or develop a character. In my opinion, that attitude shows a sort of rigidity that'll impede a writer in the long run.

I always make new characters for other roleplays. It doesn't feel right to reuse old ones, because those old characters are created of both their personality AND experience. They aren't the same when they're introduced to a separate universe. An alternate universe, sure. But an entirely different roleplay? It doesn't make sense to give two different people the same identity. It doesn't make sense at all.

I feel weird using the same character across multiple AUs, personally.

If it's within a persistent story, of course I'd rather have a persistent character, but when it comes to using the same character to fit into all kinds of different stories... I'm not really into it. It makes any character development and experiences that the character has gone through erased every time, and if you're running them in multiple places at once, it is hard to keep straight what they have gone through in each setting. So you can't really use the things that have changed the character naturally in one rp for another rp, because in that alternate world, it hasn't happened at all. Which -if you are like me and think about the character in the current, developed state- is not just insanely difficult, but also feels like a waste.

This doesn't apply to re-purposing an old, out of use character for a new rp.