They both ultimately produce BEAM bytecode, but Gleam compiles to Erlang source first (then through the Erlang compiler), while Elixir compiles to Erlang's abstract format. Gleam doesn't prevent OTP use - it has type-safe OTP bindings, but they're less mature/feature-complete than Elixir's, plus Elixir has better BEAM runtime integration (stack traces, profiling tools, etc).
Profiling tools are something that I miss a bit in gleam - yes, but otherwise I had no problems with OTP bindings. The maturity of the ecosystem is a bit lower of course. But I actually enjoy finding libraries or repos with a few hundred lines. You gotta handroll some things but that's what I am here for. ffi to erlang and js for fullstack apps is as straight forward as it gets, but erlang syntax is indeed a bit crazy. For those interested in gleam but don't want to miss some necessities: https://github.com/gleam-lang/awesome-gleam (the gleam community is super nice btw).
For me some serious elixir adventure is high up in my todo list. But I remain suspicious if I can ever fully enjoy myself with a dynamic language - I think gleam and elixir do cater to different crowds. Gleam is pure minimalism (just pattern matching really), but elixir doesn't seem bloated either.
I am so happy that both languages exist and give alternatives in times of hundreds of node deps for any basic slob webapp.
