As someone with a fairly high spice tolerance, I've found a strong correlation between heat and flavor. I think anyone coming from a culture that eats spicy food will agree.
I had a batch of habaneros I grew last summer that were both the most spicy habaneros I've had, and by far the most flavorful. I've also had some very tasty ghost peppers (when used in moderation). Outside of peppers that are inherently not spicy, such as pablanos, heat and flavor seem to coincide.
All of the most flavorful chili dishes I've had in my life have all been quite spicy, and I can't recall any mild chili dishes I've had with nearly the same punch.
The only time I've seen heat and flavor not connected is in terrible hot sauces which aim to be shockingly spices that make use of capsaicin extract.