RevitElements was my top-level namespace before I knew any better.
The release of Rhythm for fall of last year represented significant changes to the structure of the package. To help mitigate this I included a “Migrations” file in the package. This should auto-replace any nodes you have previously used under the old namespace. (Zero touch only).
The biggest changes to Rhythm in the last year is the removal of most of the OOTB custom nodes (.dyf extension). I have been trying to migrate my package to being 100% ZeroTouch and am very close.
All of the DYFs that were retired have replacements as either OOTB or a ZeroTouch version in Rhythm. That being said, if you are very attached to any of the old DYFs feel free to strip them out of the older version of the package.
I would say to get updated though! There are all sorts of amazing nodes in Rhythm that you are missing out on!