What's your biggest problems/missing features with Unity ?

If I recall correctly there are a couple of edge cases where you need to play around with the scale and font size. I've come across it once, I can't remember what for.

 

As I recall, pretty much all those edge cases were resolved with TMP.

 

Your stuff does too much in Awake/Start.
Simply move that to a different method, and give all objects an interface like `IInitializeOnCreation` where you define that method.
That's the way to go, checkout the "Ori and the blind forest" talk on youtube to see what other optimizations they did.

The only remaining problem will then be terrains because you obviously cannot abstract away Awake/Start from components that are built-in since you don't have the code. And terrains initialize their mesh data in the beginning, which causes a big spike even for medium sized terrains.