Get good at c++. Learn how to use open source 3d rendering engines like Ogre or Irrlicht. Find an open source physics engine you like. Combine into 1 program, now you have a game engine that can be developed on any os and you’ll be able to optimize your game far more than you ever would on unity or unreal.

That is a way.

Last I checked Adobe doesn’t have any 3d game engines, so that’s not really a solution, heh.

Additionally, developing a game requires many, many different parts. It’s not just the engine, it’s making the models, it’s making the materials, textures, shaders, programming, scripting, writing, and so on. Some, like 3d modeling, already have decent FOSS tools (Blender for example). Others, like the Substance suite (material authoring and texture painting) or Photoshop (image editing) don’t have a good enough FOSS alternative to be replaceable. Furthermore, many studios have specialized plugins or companion programs the studios developed or purchased which are only compatible with Substance, Photoshop, etc.

So you’re not just fighting game engines, you’re fighting every step of the process. Adobe (and Autodesk, fuck Autodesk too) products, when used, tend to be deeply embedded in most professional workflows. You’d have to replace the software and any specialized plugins or programs designed specifically to interface with the software. I mean, good luck, it’s just a hell of a lot more complicated than you seem to think.

You say they’re viable, but most people don’t want to make their own engine to make a game. Most people wanna make a game, not a game engine. Furthermore, while I honestly believe that the FOSS community could easily match commercial projects, doing so requires people to acknowledge the software’s shortcomings, talk to the professional users about what kinda UI they want, and so on. That means you can’t throw lines at them like “user inexperience” or “just learn a new program”. They’re professionals, having to learn a new program cuts into their income. Learning new programs means they aren’t making things, which means they aren’t making money.

I know I’m kinda rambling a bit and may not be super coherent (if so, I apologize, I’m running on low sleep), but I’m not trying to be a doomer or say “that’s impossible”; I think what I am trying to say is that I don’t think the FOSS community currently has all the necessary software features or ease of access for professionals.