I also agree with this - I find it particularly difficult to maintain apps that I wrote for an earlier version of Rails, and which I had to lock to that version

I also agree with this - I find it particularly difficult to maintain apps that I wrote for an earlier version of Rails, and which I had to lock to that version to avoid the app breaking in hard to diagnose ways; I sometimes don't touch these apps for a year or two, and working on them again means remembering the idiosyncrasies of that particular version of Rails, which are different from the idiosyncrasies of the version of Rails I'm using for another more recent app I'll be working on. In fact, it's bad enough that I've been looking for alternatives to Rails for each new project I've started in the past year or so, but always give up because I think it'll be quicker to use what I know (and then usually end up regretting it later.)