It's certainly "high quality" in the sense of "it solves a huge number of requirements that WP core doesn't, in a way that's better that alternative plugins". It's a high quality WP Admin user experience. Just don't try looking too deeply into the database mess it creates.
For WordPress _users_, as in the people who log into the WordPress dashboard to run their website, 'stuck in the past' is often an advantage and not a bad thing. You'll be able to find blog posts and tutorials and youtube showing you how to use in, unlike the "new shiny" where there's no easily found example or support for.
I'm not arguing against its usefulness, not at all. The sites I work on use it as well (and abuse, you really shouldn't do complex things with it), though we're looking into replacing it with something custom because the dev experience is bad and the performance isn't great. But for the average small to medium site, it's great, especially because of what you mention: the standard use cases are super well documented by a million people having gone through them before you.
I wouldn't call it high quality though. 200k LOC even for the free version (I use pro), no OOP, global variables, bugs get no attention unless they're major. It was amazing when it first came out, but it has fallen behind even compared to core + other plugins (and the WP average is a very low bar).
It clearly belongs in core, just like 90% of Yoast's (or AIOSEO's, Rank Math') functionality, Redirection and permalinks, and they should have focused on getting that done instead of gutenberg. But also clearly this isn't the way to bring it into core.
For WordPress _users_, as in the people who log into the WordPress dashboard to run their website, 'stuck in the past' is often an advantage and not a bad thing. You'll be able to find blog posts and tutorials and youtube showing you how to use in, unlike the "new shiny" where there's no easily found example or support for.