Frazetta's art is full of tension [1] and energy [2] whilst Vallejo is simply drawing his circle of bodybuilders in various poses. The environments he paints have absolutely no effect on his posed subjects and the end-result is disconnected and comes across as "fake" in its intended setting as it evokes memories of bodybuilding gyms.
[1] https://www.frazettagirls.com/cdn/shop/products/frazettagirl...
[2] https://frank-frazetta.pixels.com/featured/the-destroyer-fra...