RE: X/Y Box Art Subtly Reveals Legendaries Typing?
Yes, that, and also the fact that there's more than one class of legendaries:
-those who's power is so great that affects the entire world:
(articuno, zapdos, moltres /weather (according to the movie), lugia/oceanic currrents, ho-oh/sun, groudon/landmasses, kyogre/sea levels, rayquaza/atmosphere, palkia/dimensional space, dialga/dimensional time, giratina/dimensional nothing, arceus/creator)
-those who are just really powerful and rare:
(mewtwo, celebi, deoxys, regigigas, victini, reshiram, zekrom, kyurem, tornadus, thundrus, landorus, genesect)
-or just powerful:
(entei, raikou, suicune, regice, regirock, registeel, heatran, darkrai, cresselia, cobalion, terrakion, virizion, keldeo)
-or rare:
(mew, latias, latios, jirachi, manaphy, phione, shaymin, meloetta)
Of course, all are special, and all are rarer than a regular pokemon; some of them are very few or even the only ones of their kind (mewtwo, genesect, reshiram, palkia), while others could be more than just a few, but still rare (the trios, lati twins, darkrai, manaphy/phione, shaymin, meloetta)
I probably made some mistakes, and the specific rareness and power could be argued for years, but the pattern is clear, I don't think anyone would dare to compare the magnitude of dialga's power to registeel, for example (always talking about the specific powers, not battle matchups)