The pictures for Troll and Ogre may have been switched ... just as long as Ogres look bigger and tougher in game, the picture comparison might not have translated well.
And as far as different species that are very close in Phenotype, I don't mind a difference/ diversity. For me its as cool as Ogre vs Bone Ogre, or Black Widow vs Rock Spider, or Forest Drake vs Swamp Drake vs Mountain Drake vs Shard Drake.
anyways, its a difference in preference. Differences in strength, speed, rarity, environment, and (habits?) is a bit of a plus for me ... and there is already a variety of physical forms in place, so a few "closely resembling" species is perfectly fine. Also, anything slightly related to a Dragon will have a similar appearance ... and thus far Drakes, Slags, and Dragons are all cool in their own right (and the smaller ver. of Drakes sound rather cool as well).