Much as I love open source and the Godot engine, this seems more like a wake-up call on the importance of corporations not being able to unilaterally, retroactively change contracts in ways that impose new charges and violate existing contractual commitments that others have relied on. If they can do that then open source doesn't offer much real protection.
Open source is that protection. There's no way for an open source project to change their terms that drastically. The whole hasicorp disaster is a prime example of that. Terraform is forked and continues on like normal, users are not impacted. For programming platforms (like game engines) this is even MORE of an advantage, as with something like terraform you could conceivably rewrite your stuff in a matter of weeks…
That's a massive overstatement of the current state of OpenTF right now. Plus they're still dependent on Hashicorp's hosting which also changed their license terms in response to the project.
You're right that because it's OSS you can do this kind of thing where it wouldn't be possible at all in a proprietary system but "just fork" requires a community to organize around it. Without a bunch of backing orgs this wouldn't have happened.