Tarkov is a bad example. The devs are absolutely FLOGGING the entity count and their maps are huge with lots of little details. People give them crap for doing a bad job but the vision they have for the game would be difficult to pull off no matter the engine. They have been on an old version of Unity for a while and are currently moving to a newer version.
One big argument people have is whether the lighting in game is good or not. They do dynamic lighting, which can definitely cause some voidlike shadows, but people were arguing over whether Unity had tools to help with that or not.
Also, multiplayer is hard, but they have made some (very questionable) decisions like sending all clients the entire map entity list. Hackers abuse this to know where rare items are located and even the stuff other players have found or brought into raid. If I find a GPU or LEDX and put it in my bag, they instantly know and can come kill you to take it. This combined with issues with desync, audio not working correctly, invisible players...I don't think this is a Unity problem as much as it's just a complex game, a pretty small dev team, and they don't want to hire outside of Russia.
Tarkov, while a great game, is very janky, and has a cheater problem. I have heard these things attributed to Unity, though I am not familiar enough with the details to say that's absolutely true.
Rust is fine though, in my experience. (and yes I do mean the video game in this context, hahaha)
One big argument people have is whether the lighting in game is good or not. They do dynamic lighting, which can definitely cause some voidlike shadows, but people were arguing over whether Unity had tools to help with that or not.
Also, multiplayer is hard, but they have made some (very questionable) decisions like sending all clients the entire map entity list. Hackers abuse this to know where rare items are located and even the stuff other players have found or brought into raid. If I find a GPU or LEDX and put it in my bag, they instantly know and can come kill you to take it. This combined with issues with desync, audio not working correctly, invisible players...I don't think this is a Unity problem as much as it's just a complex game, a pretty small dev team, and they don't want to hire outside of Russia.