Having used Heroku at multiple startups during the 2012–2015 years, this is not correct.
With heroku you could `git push heroku master` and it would do everything else from there. The UX was nice, but that was not the reason people chose it. It was so easy compared to running on EC2 instances with salt or whatever. For simple projects, it was incredible.
That's literally the UX I'm talking about and that's what other companies copied too. To be clear, I'm not (just) talking about how heroku.com looks and works, I'm talking about the entire user experience including git push to deploy, so I believe you are agreeing with me here. That is why I said VPS with Dokploy or Coolify and so on have the same UX, both in the command line with git push deploys supported as well as (now, at least) a vastly superior website user experience, akin to Vercel.