[1]: https://ocamlpro.github.io/drom/
What’s wrong with opam? Since version 2 it also supports local switches and locking, and the opam repository has become much more stable than in the past. Full disclosure: I am biased here, since I am one of the opam-repository maintainers and I am quite happy with opam itself.
I'd say the main problem is that local switches and lock files are still not the default mode of operation.
Also opam lacks a global cache of built packages which esy provides (esy's cache is modelled after Nix package manager). So every new opam local switch effectively compiles everything from scratch. Though, as I understand this aspect is going to be addressed by dune at some point (though esy caches not just OCaml built artefacts but also C/C++).
(Full disclosure: I'm biased as I'm one of the original developers of esy)