Who cares if Josh makes Roy better? I think Roy's made a pretty clear this year through his play that he might be a solid center who will have some good stretches, but he is not the long term corner stone of your team. Basically, you don't decide who else to start based on Roy Hibbert.
Tyler has helped the Pacers win more. Roy and Danny are like yo-yos. Their stats in wins and losses are polar opposites. Tyler doesn't see nearly as much variation...in other words, he's actually been much more consistent.