DHH's most recent hotwire update...
Evan You who created Vue and Vite had some comments on it: https://twitter.com/youyuxi/status/1425933472871456777
He's specifically referring to larger frontend applications and I think those are valid points where Webpacker, Vite, or an alternative will still be the best option.
So it sounds like it depends on what you need. Importmaps will be perfect for applications that don't have a ton of frontend dependencies. I think Rails has always pushed for minimal JS, so it makes sense to use importmaps out of the box.