Andre Drummond has proven, at the bare minimum, to be an NBA level defender/rebounder which is more than Jeremy Tyler had shown playing abroad.
Even if Drummond fails to develop well, he will be, like Kwame Brown, a decent starter / high level backup center in the NBA. Meanwhile, if Jeremy Tyler fails to develop, he'll at best be a third string center, or, more likely, end up out of the league within a few years.
That all said, I agree that Tyler went too low in the draft. Anytime you get a big man with his youth, size and athleticism ... he should be a first round pick (ditto with DeAndre Jordan). Too much upside to ignore. As for Drummond, ideally, I'd say he is more of a late lottery to mid first round pick (like Andrew Bynum when he went #10).
Also, I am surprised to see any praise for what Tyler did last year for the Warriors. He was god-awful. He had no ability to defend his position or comprehension of how to play team defense. His offensive game was extremely limited and his rebounding was well below par. He was one of the worst players in the league last season. He was a massive liability.
But you knew that when you were drafting Tyler, that he was going to take time and need a great deal of work before he was ready to play to be a positive contributor. So, even though he sucked, it doesn't mean that he won't be a useful player down the road.