You have to constantly fighting Unity to get the performance you want, which is extremely frustrating. The time spent on figuring out "WTF are you doing Unity"

You have to constantly fighting Unity to get the performance you want, which is extremely frustrating. The time spent on figuring out "WTF are you doing Unity" and coming up with a workaround is huge. Inside had a talk about how they achieve smooth seamless gameplay which involves purchasing access to Unity source code and mod it.