Check out Rust and Escape from Tarkov, they are a big step above your typical Unity games. So even if its not their core userbase they certainly have such titles already, and it seems that they want more.
As someone who bought it 4+ years ago in alpha it's a game that has come a long long way, same with rust really. Its not without it's issues, hard to say which are engine problems or just bad decisions made by the devs, which is hard to blame them for as their situation is a bit different compared to many other game companies.
If you actually read the case study, there are 0 mentions of Unity. This PDF is about Multiplay (acquired by Unity in 2017) and the backend; the game is on a highly modified Source engine.
