I'm currently in the process of switching from YouTube to Piped and was getting fed up with rewriting YouTube links myself. I finally found an extension that can do this with a relatively easy setup:
There is an extension called LibRedirect that does this. It's customisable, as in, we can set if we want to redirect to piped or invidious, and which specific instances to use. Not only just YouTube but other services like GitHub to Gothub, Twitter to Nitter, reddit to libreddit etc. The default settings are already great.
It is, but it already has all the services that most would use with big QoL features compared to Redirector. Namely quickly adding and removing instances, and quickly enabling and disabling redireciton for specific services. And is a lot easier to use in general especially for people who don't know regex.
Plus Libredirect has a few features that redirector doesn't, the ability to redirect to multiple different instances, and the ability to redirect embedded content such as any embedded youtube videos on any other website.
But as you said, redirector is more flexible if you need it for something other than the ~20 services that LibRedirect handles.
All of this only makes sense if you're redirecting to a frontend, right? Not an alternative platform? For instance, it would be nice to redirect all Goodreads links to Bookwyrm, but I'm not sure if this is possible. (Already got it set to redirect to Biblioreads, but just curious since Bookwyrm is what I actually use.)