The language should have defined a consistent async model (like coroutines with message passing) and kept "raw async" confined to high performance special libraries and embedded use cases.
It is quite unfair to complain on convenience of Rust async used with no heap allocations to other languages which don't offer an option to avoid boxing at all. In e.g. Java when you return a Future it is always on the heap. In Golang, you don't even have a Future concept. So you basically can't do the same thing in other languages at all.
Like I am positive we'll be getting GAT misuse / abuse just by sheer accident because people don't understand them (they're a complex language feature), just like we have libraries going async needlessly.
It will also not fix the "lifetimes for async functions are special" issue, due to the lazy evaluation of futures, and the "async functions might sometimes stop executing in the middle" challenge.