XML/XSLT/XPath are great, but XSLT ecosystem has been effectively "frozen" for over a decade in terms of innovation and tooling. The last major step was XSLT 3.0 (2017), which introduced streaming and function integration. However, in practice, no new engines or radically different approaches have emerged since then.
And there is only one free XSLT 3.0 processor available, SAXON-HE (it lacks schema-aware & streaming though)
Even worse, in practice you still often only get to use XSLT 1 and XPath 1, because that's what the common Open Source libraries (i.e. libxml/libxslt and Xalan) typically used to embed XSLT into Software support. (The existence of EXSLT should better be forgotten). For anything else, esp. dedicated standalone XSLT development, there is basically only saxon. I wish, there was better Open Source support for XSLT/XPath 2+ but i don't think it's likely to happen.