Amdahl's law was about the potential speedup from going parallel being limited by parts that must be serial. Nothing controversial here - many tasks can be parallelized just fine.

My point is that you often see a simpler algorithm/data structure in C for fear of a memory issue/not getting some edge case right.

What part are you disagreeing with? That parallel code has more gotchas, that make a footgun-y language even more prone to failures?