You know people are going to glamour skirts on regardless.
Fenrir was only a Dark-Elemental in FFXI. He was an Earth-Elemental in FFIX and a Non-Elemental in FFVI. His role was never defined outside of FFXI, so they can make him whatever they want in this game. Alexander would be a hard sell to change up, as he's not only always been a Holy-Elemental, but he's always held a somewhat prominent role since Final Fantasy IX.
Garuda is the only exception to what they added. Titan/Ifrit/Shiva/Ramuh/Leviathan/Odin/Bahamut have always been iconic (exceptionally recognizable) summons through out the Final Fantasy games, hence they were given much more priority over everything else. There has never been a well defined Wind-Elemental summon, so they threw Garuda in there from FFXI and called it a day.
It was never about what summons had more or less "power", because this definition almost always changes between games (this and the fact that summons rarely got story lines & side stories outside of Bahamut and Odin). It's all about what they deemed is an "icon" to the series and IP.
