Yeah, it doesn't have to be that way, but it so often is. I like the Herndez brand mexican salsa you get at the grocery store (US), but the flavor of the medium is so much better than the flavor of the hot. It's like with the hot ones, the only care about getting the heat.

I've had very hot sauces that had really good flavor, it just seems more rare.

That should be the default spicy, so when I say 'very mild' it's doesn't turn out sweet.