Not ex-Stripe but in "close relationship" with them since its inception and there's a clear mark in my calendar circa end of 2018 when their decisions and output started to become... weird, or ill-designed.

I don't think it has to do with the dev environment itself, but I'd blame such thing for allowing to deliver "too fast" without thinking twice. Combine that with new blood in management and that's an accident waiting to happen *

They're the best in business still, but far from the well-designed easy-to-use API-first developer-friendly initial offering.

* Pure speculation based on very evident patterns