I agree that concurrency isn't fundamentally hard, but the reason everyone kind of prefers faster serial execution is because a lot of algorithms (extremely simple example: f^100000(x)) are fundamentally unparallelizable. Faster serial execution is just so much more straightforward.
So a common problem with concurrency tends to be not "How do I make these functions run in parallel", but "Is there an algorithm that does the same thing I want without relying on constant function composition?"
So a common problem with concurrency tends to be not "How do I make these functions run in parallel", but "Is there an algorithm that does the same thing I want without relying on constant function composition?"