Setting up a python server environment seems to be hard work, with lots of steps (gunicorn and all that) but that said they make the point about using Docker. So maybe docker compose could take a lot of the pain out of it.
https://libcloud.readthedocs.io/en/stable/compute/drivers/di...
So as long as you don't mind writing your deployment scripts using Python you can make them reasonably portable (though honestly every provider has a little bit of quirkiness that needs to be worked around but it's usually trivial stuff).
Should solve 95% of that "lock in" problem.
One advantage from DO is the regular backups.
Like you said, you can go for executing docker compose on the server if you want to do it fast.
I find it just as easy as Heroku, but cheaper. As someone who hates messing with servers and prefers to focus on my product, render is perfect for me.