It creates 2 disparate types of error handling that don't neatly mesh together. You have to handle error return values, but you also have to handle exceptions (panics) because they still exist.

My issue is mostly implementing both ways of bubbling up an error to somewhere it can be handled. I think having either error return values or exceptions is preferable to having both. I don't think exceptions are perfect, but if panic() absolutely has to exist then I'd rather have an entirely exception-based language than a language that uses both systems simultaneously.

E.g. if I write a function that accesses an element of an array without bounds-checking, it could panic and I have to handle that exception. Bounds-checking basically just becomes finding things that would throw exceptions and converting them to errors so we can pretend that exceptions don't exist.