I've worked on a lot of legacy Rails apps. Most of the problems of "spaghetti code" occur because people write bucketloads of un-Ruby-like code that betrays a serious lack of understanding around how Rails really works. Whenever I hear "aw man, Rails sucks. I switched to writing (X) in Rust/Go/Haskell/TypeScript/whatever…"

Let me stop you right there. If you tell me Rails wasn't meeting your needs so you rewrote (X) in a different manner using Ruby + something else, I'd totally understand. Otherwise, all it tells me is that there was a tragic lack of deep Ruby knowledge, respect even, to begin with as the project unfolded. Often I muse on how in some ways it was unfortunate that Rails became such a darling in the startup community early on. It meant that a ton of people jumped into Rails web dev thinking they were writing "Rails". No, you're writing Ruby, and Rails just provides a nice set of base classes and some decent defaults and assumptions. If you end up with a giant wad of spaghetti mess, that's on you. It's totally feasible not to end up there, and plenty of projects end up in far better shape.