Good at smaller scale, and Heroku can go pretty good at scale. But eventually you run into things that they make harder rather than easier if you need to do something which doesn't fit well with their model. Deploying onto Google Kubernetes Engine has a bit of boilerplate setup work, but after that it's not a huge management overhead considering everything it gives you.
Okay, yeah, for sure. I think they're better options for early iteration. I guess actions speak louder than words here since my preferred operational stack is Rails + Typescript + React + Redux + Heroku w/ Heroku Postgres.
Yeah, definitely Heroku over k8s for idea validation.
I think there's definitely room in the k8s-based space for slightly past that, though.