Of course, open source projects regrettably become closed source projects sometimes too (see Hashicorps recent moves), locking you into the previous version of the project.... but, with Open Source, you can fork the project and continue- or ally with other members of the community to fork- often at a lower cost than re-training and re-tooling. An option that does not exist in the proprietary world.
You'd be hard pressed to compete with Epic Games' investment in the engine for their own games and others, too. I don't think this situation is comparable with Hashicorp. Epic has more than a hundred engineers continuously improving the engine, doing research on new technologies like Nanite and similar, and all their improvements are available to you immediately. You have full source code available and are able to modify it as needed, you can also fork it under the current terms. As far as I know there were never any forks with significant traction, only to implement random features people needed in their game.
This is just a guess, but I truly don't believe we are going to see Epic Games turn evil like Unity has as long as Tim Sweeney holds more than 50% of the shares. Going public was Unity's death sentence - the tech no longer mattered, now it was all about extracting the maximum value possible before the company is run into the ground.
