I think this is not a fair assessment, GitLabs community edition is fully open source and is a full product. The fact you can add proprietary elements for a licensing fee (which are also "open" in that they are readable, debuggable, etc;) is not at all the same as hosting on a platform which is entirely proprietary.
[1]: https://salsa.debian.org/help [2]: https://gitlab.gnome.org/help [3]: https://gitlab.freedesktop.org/help
While gitlab.com is based on the Enterprise Edition version, it's 100% possible to host into FOSS only if you wish.
2. What does the registration process look like?
OAuth helps with federated authentication. It's not federated registration.
2. Click “sign in with provider” log in as normal, or just get logged in if you have a cookie.
3. These are functionally identical, it’s 2 clicks to create an account on gitlab if you use an external identity provider.
I’m pretty sure it’s MIT. This page says it is.
How easy it is to actually do that depends on your ruby skills and your wallet.
Usually when people say this they are referring to either Gitlab or Gitea. Well, it's not like all of Gitlab is fully open source, it's just Open Core, but I'm sure that's a sizable amount of the code, but I would imagine there's a decent chunk of gitlab.com source code that's proprietary (I'm sure somebody will quibble with this in a following comment, but the original argument is an argument of purism of being free and open).
Gitlab CE and Gitea doesn't solve the hosting issue, though of course Apache could probably pay somebody to manage that, but then you've introduced extra overhead for collaboration that most people aren't that inclined to solve.