Compare Vallejo to Frank Frazetta and it's immediately obvious why the latter is considered a master of fantastic art while the former is drifting towards obscurity.
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...
You might as well be comparing Slayer and Cannibal Corpse. Both styles have their place and they can be enjoyed in their own right.
I prefer Frazetta too, but Vallejo is rightly recognised as one of the greats. He does his own thing. Not everyone can, or should try to, be Frazetta. That'd be pretty boring.
Or, like I once told a friend: you gotta stop comparing everyone to Bugs (Bunny).