Om came first, Cloact (eventually renamed Reagent due to an unfortunate similarity with a certain body part of a snake) came after it.

Here is the original HN post about Cloact: https://news.ycombinator.com/item?id=7037038

You can see people comparing it to Om.

Here is a blog post of his from 2013 that mentions Om: https://swannodette.github.io/2013/12/31/time-travel/

And yeah, Reagent "won" because it was way simpler but I'd find it hard to believe that it wasn't influence or inspired by Om.