Counter-argument is: do you really want some team of 90% marketers and PMs throwing up a MVP/WIP codebase for some ancillary product not related to your core business on your core domain? At a minimum you'd want a thorough security review and risk assessment, and that goes against the ethos of "ship fast and pivot as needed".
I mean, it sounds like they're already doing that, just with extra downside
Why does the TLD matter in this case? How does your security/risk posture change if you launch on myexperiment.mycompany.com vs. www.mycompanyexperiment.website that you had to go out and newly purchase? Asking because I legit don't know.