I wish that transparency and security were a selling point in gaming, but to me it doesn't seem like it. People will install all kinds of stuff and give them administrator permissions without a second thought. Anti-cheat eating itself into the kernel seems to be perfectly normal for most people. It's an entertainment product and people don't want to be inconvenienced for the most part.
Regarding the development costs, I'm not exactly an expert and I have never worked in a game studio (apart from the company my wife and I are running), but let's take StarCraft 2 for example. If you were to have the engine, but not the art, you could likely easily develop a very capable multiplayer RTS game. Heroes of the Storm was developed out of a StarCraft 2 mod[1]. As another example, Stormgate[2], made by ex Blizzard devs, is getting a whole lot of press coverage for their netcode. It stands to reason that a good engine and netcode are very real competitive advantages in the RTS space. Other game types, such as a walking sim or an adventure game will have a lot less "secret sauce" in the code and more in the art, voice acting, etc. (The Invincible[3] is great in this area) so the code/data split would likely heavily depend on the type of game. (Games can also become very messy between art, visual scripting, engine settings and code, which is what makes releasing the code separately tricky.)
My wife and I are (slowly, next to the day job) working on a Python programming/learning game and hopefully we'll manage to make a clean split between the engine and the art because it would be important for modding. However, I wouldn't feel comfortable releasing it under an open source license because it would cut off a potential source of revenue to license it to educators wanting to make their own challenges and courses. Maybe later we'll figure out that the base game makes enough money and it doesn't matter anymore, but it's really hard to predict success. As a game dev I would really like to make it possible, for example, for game archivists to do their work legally, for people to legally backup and rebuild their games for newer operating systems, or for their kids to be able to inherit their games[4], but carving out specific exceptions, especially for unknown future use cases 10-20 years down the line is exceptionally hard and I'm also not a lawyer, so for desktop the Steam Subscriber Agreement is governing our PC releases for now.
[1]: https://starcraft.fandom.com/wiki/Heroes_of_the_Storm
[2]: https://www.pcgamer.com/an-upcoming-rts-will-incorporate-the...
[3]: https://store.steampowered.com/app/731040/The_Invincible/
[4]: https://arstechnica.com/gaming/2024/05/after-you-die-your-st...