Regarding Lopez, he did average 20ppg in one season and averaged 19ppg before and after his 20ppg season. It's not as if he scored 30 points against the scrubs and then 10 points against the elites.
This was his game-by-game stats during the 2010-2011 season:
I see a lot of big games against the guys that you mentioned. Including a 35 point game against Bynum which he limited to just 2 points.
He has a wide array of moves and he doesn't rely on strength and this is why a lot of experts are saying that he's one of the best OFFENSIVE big men in the game. If he averages a couple more rebounds more, I'm sure he'll be included in all-star considerations. I can see him averaged 9 rpg, something that he's already done, this year. This is because he won't be pressured to score in bunches anymore.
Perkins had a disappointing season with OKC but I guess that's mainly because of too much pressure to be that imposing veteran. A change of scenario with the Nets, where there are a lot of veteran presences, might do wonders for him.