So Chromium-Edge was basically an admission from Microsoft that they're bad at making browsers...
No, it wasn't. In among all the proprietary Active X crap there was, at least with IE ≥ 9 some reasonable code and the IE team did make some significant contributions to the HTML and CSS test suites, though it didn't seem to want to support SVG or other video formats, that it wasn't in the patent pool for. The problems were not really with the rendering engine but in the fucking brain dead twins of bundling the browser code in the OS file manager (and Outlook), and nurturing privilege escalation attacks through Active X plugins, which were always exploits waiting to happen.
But, developing a browser rendering engine is a lot of work and Microsoft had realised that it could achieve lock-in in other ways. So, by switching to Chromium it could pursue lock-in and sack a load of developers and QA and let Google do the work on the rendering engine, which it now uses for more and more subscription products.