I don't think it would have been strange if the Legendary Birds kept/got the following:
G-Articuno: Ice Beam (I mean it shoots a beam from its eyes that have a freezing effect),
Icy Wind (Have you seen what Pokemon can get Icy Wind
via TM27?)
Normal Articuno: Psychic, Psyshock, Calm Mind (Now that see under a certain condition Articuno can become a Psychic-type, I don't think it would be farfetched to say it could access some of the basic Psychic-type moves that many non-Psychic Pokemon also get via TM),
Shadow Ball (I just feels like common coverage that most Special-types get so why is Articuno exlcuded?)
G-Zapdos: Wild Charge (With it now actually charging everywhere it makes even more sense for it to have it),
Roost (It's basic healing move for any bird Pokemon; it still has the Flying-type to lose)
Normal Zapdos: Nothing really, at least from what G-Zapdos learns.
G-Moltres: Heat Wave (Many winged Pokemon learn it),
Mystical Fire, Will-O-Wisp (it's not normal fire, it's mystical fire so that's vague enough for supernatural Pokemon to learn it),
Roost (It's basic healing move for any bird Pokemon; it still has the Flying-type to lose)
Normal Moltres: Dark Pulse, Snarl, Nasty Plot (If it can be turned into a Dark-type then it's normal form likely has enough to release some dark energy),
Shadow Ball (I just feels like common coverage that most Special-types get so why is Moltres excluded?)