Yes, he really is just built different.
As for sources? Repeatedly he is stated in multiple sources: in the
Myth to Legend bonus video,
GOW1 PS2 Manual and
GOW2 PS2 Manual (Where Poseidon is stated to be second in eminence only to Zeus),
GOW1 game itself in the Zeus' Fury obtaining scene, and in the
GOW2 novel (This is where he angrily states that anyone who even thinks to betray him will be reduced to ash by his lightning bolt, and he threatens that as King he can do anything he pleases, even go so far as to violate the edict to not harm any gods, an edict he himself made up to avoid another Great War), to be the strongest and mightiest of all the Olympians, and that nobody can ever hope to challenge him in combat. The Three Olympians (Zeus, Poseidon and Hades) are stated
to be unrivaled and unchallenged, that they are the strongest of all the Olympians, even in the GOW1 novel (The Three Olympians are called the Brother Kings), and in the GOW2 novel Zeus scares Hades and Poseidon shitless just by getting enraged and raising his voice,
thrice in a row.