I'm banking that Delphox has a limited move pool due to her new type comboa for a starter. Look at Blaziken, leveling up it's best moves were Flamethrower and Sky Uppercut (iirc) originally, and the TM coverage in ruby it got really extended to Rock and Ground (maybe Flying if you liked Aerial Ace). Blaziken was a new combo at the time, and the waters were being tested. Infernape had a wider movepool than Blaziken, and Emboar holds the title of being the only (currently) available Fire Type with a Water attack (new steam legendary will beat that out in a weird way).
I figure Delphox is the testing of the waters for it's combo, as a Starter Psychic is a pretty decent offensive type ingame. Defensively, well Darmanitan and Victini showed us what they had...
Sig Strike #4.
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