I'm sorry but to classify Leona as an AD Carry/Bruiser is not correct. Not all champions are meant to deal damage and carry, some are meant to support and cc. Leona being an example herself, with others such as Blitz, Nautilas, Nunu...
You may say there is no need for a support player in 3's but you would be mistaken. I'd like to see 2 straight dps bot try to vs a good support and a dps early game and not come off on the losing side of the lane.
Overall these Champions should have a tier list of their own and not be classified under how well they can damage but by how well they can properly cc, take damage, or in general support their team.