> a system that will lead to unexpected bottlenecks when you parallelize

This is a funny comment. You are implying that performance is of higher value than correctness. Speed without correctness is dangerous, and leads to significant bugs, especially when you're talking about concurrent modification of state across threads.

I'll take correct and need to improve performance over incorrect and fast where the cost of tracking down incorrect concurrent code is so extremely high, let alone dangerous for actual data being stored.