I'm not saying pokemon above50 shouldn't be scaled down, but given how we as players gain dragonite/Tyranitar, they shouldn't be scaled down as they don't exist within the means of the players. However say a Salamance is level 53, it should be able to be scaled down. However Dragonite/Tyranitar doesn't exist below level 55 that is in the means of how a player can get them. Also for all we know, GameFreak/Nintendo scaled the dragonite down to make it easier to face Lance.
Also Lance is a master of dragon types. So for all we know he knew how to evolve his pokemon early.
Also over leveling your comps shouldn't be an issue, again you don't need to use comps to do anything outside of PvP/Battle Frontier/Trainer Tower. Don't use your comps in other scenarios and the problem won't be a problem.