"I'm superficially familiar with Haskell's typeclass system, but respectfully, this misses my point."

I suggest becoming more than superficially familiar, then. With all due respect, I believe your core problem is that you do not understand what advanced type systems can do, so it's a mystery to you why anybody would want them, and the only cure for that is to go learn. Again, let me emphasize, I do not mean this to be mean, but sometimes there's just no way around the problem in an HN-post sized reply.

I know one recurring thing I've encountered is that I'd love to be able to say that in

    type Something interface {
        DoWhatever() Something
    }

that the return result of DoWhatever is guaranteed to be the same type as the thing you called it on. I'd love to be able to guarantee that if I have a container and a contained type that I can associate the two things together (i.e., I have a "Game" and "Move" interfaces and I'd like to associate specific Game implementations to specific Move implementations). I'd like containers that don't wrap everything in interface{}, resulting in an inefficient representation that is also hard to use in the code. I'd like non-nillable pointers.

On the balance I still use it for my job because the benefits outweigh the costs, but there are tradeoffs I make for it.