I don't know if that's true in general, but I know that most people consider Kentucky bluegrass to require full sun, and it does a lot better in my shaded back yard than in my sunny front yard.

It depends on the plant but for sure, most of the time the answer to your question is yes.
Our elevation increases the UV exposure and to many plants, it's too much.
It can be a complicated question though, because in addition to our increased solar radiation, we also have more alkaline soil and less humidity than most other places.

Full sun means 6 or more hours of sun each day. For grasses KBG is a bad choice for utah! A fescue or rye grass is a much better choice as they use less water and stand up to the dry heat we have here.