My experience since the changeover has been that the Adobe-based PDF Reader in Edge is slower in every way - loading, rendering (especially), and searching.
My local city council's monthly meetings include a 50-100 PDF containing the agenda, and when loaded in the "legacy" PDF reader, the first page loads instantly and subsequent pages load within a second or two, especially if I read from top to bottom. With the Adobe-based one, I can be waiting closer to 20 seconds, even on early pages (and the further down the page is, the longer the wait). Additionally, with the latter, if I search in such a document, it will take a while to find results, and when it does, scrolling to those results renders a blank page for a frustrating length of time.
I am personally very much against the removal of the old PDF reader. Just because Adobe makes the new one, doesn't mean it's better.