It's not a question of whether it is centralization and will be, it's a question of how much. And realistically it will be too much unless there is another freak development. There's too much money in a small group of hands, too much work landing in a single place, and too much control landing on single shoulders. Sure, it's still transparent and a solid concept, excepting that it barely buys anything, but it's headed right towards centralization as smaller miners and transaction processors drop off into oblivion.