I'm familiar with both - but not really the same order of magnitude. crates.io lists >120k packages. opam has ~4500, and stackage ~3000. And the package ecosystem is only part of it. Admittedly, I haven't written any OCaml or Haskell in the last year or so, but my experience of just getting a new library or executable up and running isn't comparable to cargo either. But also hard to separate my strong familiarity with Rust from the comparison.