Elton Brand wasn't that explosive, what he had/has is an absurd standing reach. And West wasn't overly skilled coming out of College, he worked to improve his mid-range shot which allowed him to play the PnR with Cp3. He's from the same mold in that if he's 6"9, he'll be average height for a PF, burly and will need the mid-range jumper as his first weapon to build off of.
Demar took a step back last season, but he's still talented and he's better than Young. I pointed out MKG is the best case scenario, even though I don't know how he would play with Demar

. If Barnes and Perry are on the board, honestly I take Perry just because of the higher ceiling, sure he could be a bust but in this case both are Sophs, both had underwhelming seasons but Perry has more room for improvement.
I didn't say Perry would turn into a great shotblocker, he could clean-up on the weakside though and being better than Bargs as a shotblocker doesn't really require much. He could improve simply from no longer having to guard PF/Cs anymore.