I would say the most annoying bit is around javascript. For example I would like to move a rails 6.1 project to 7, and also replace webpacker with esbuild. I'm pretty sure I will just create a fresh 7 project and start copy pastaing files over, then do the javascript stuff delicately (the default javascript setup in rails 7 is also quite strange)
But upgrading pure API Rails projects is much less painful
The Webpacker removal in particular was a huge pain for me. I was deeply frustrated by DHH’s belief that the framework no longer needs to support TypeScript.
But upgrading pure API Rails projects is much less painful