My biggest problem with XSLT is that I've never encountered a problem that I wouldn't rather solve with an XPath library and literally any other general purpose programming language.
When XSLT was the only thing with XPath you could rely on, maybe it had an edge, but once everyone has an XPath library what's left is a very quirky and restrictive language that I really don't like. And I speak Haskell, so the critic reaching for the reply button can take a pass on the "Oh you must not like functional programming" routine... no, Haskell is included in that set of "literally any other general purpose programming language" above.
There's clearly value in XSLT's near-universal support as a web-native system. It provides templating out of the box without invoking JavaScript, and there's demand for that[1]. But it still lacks decent in-browser debugging which JS has in spades.
[1] https://justinfagnani.com/2025/06/26/the-time-is-right-for-a...