Hello, I found this interesting to read (although I did not understand the details), maybe you will find it interesting as well.
Question on Quora: Why don't big game companies use Unity for their game development?
Answer on Quora by Mark Maratea (Client Architect - Gameplay):
(Answered Oct 30, 2015.)
Upvoted by Gage Randall, Founder | Managing Director at Devious Gamers
"There are a few reasons but the biggest one is scene serialization and nesting prefabs.
Unity is great for 1-2 people. Its decent for 3-10 people. When you want to make a big game you have 100s of people using the editor.
Today I had an issue one Unity project we are runing where someone else checked in a prefab. I synced P4 and got the change but 1/3 of the new serialized elements were null in the inspector. Odd. Eventually I just shutdown and restarted the editor and it magically fixed itself. About half
the (of 20) had this problem. I figure it cost us around 15 man-hours. We've had metafile import issues causing scenes to lose their scripts requiring a unity asset reimport - which takes 90min or so depending on the machine specs and the project. We have a lot of assets and scripts.
Frankly that is all bullshit and unaccpetable for a professional project. I'd estimate we burn around 20% of our week on "unity issues." Some weeks are far far worse than others. It also leads to tons of "works on my machine" issues which drag even more people down when there is a bug.
For BIG games Unity is an even worse choice. Unity uses floats for the Vector3 class. For something taking a ton of area there is a huge precision problem at distance. You can work around it by floating the coordinate system as you move but that is an ugly hack and still causes many issues. Since you don't have source code, you can't even convert the engine to use doubles. So large worlds are effectively out (again, you can work around anything with enough time/money but the quality bar is usually lower when you have to make tradeoffs at the fundamental levels of the game)
I've made small 2-3 person projects that went extremely well. Unity was a perfect choice for that."