Well, here’s a quick comparison between a half-orc Fighter and an equivalent level ogre mage at 1st and 6th lvl:
Half-orc Ftr1:
Abilities: +2 Str, -2 Int, -2 Cha
BAB: +1
Hit points: 10 + Con
Feats: 2
Skill points: (2 + Int) x 4
Base speed: 30 ft
Special: Darkvision, orc blood
Ogre Mage1:
Abilities: +2 Str, +2 Cha
BAB: +0
Hit points: 8 + Con
Feats: 1
Skill points: (2 + Int) x 4
Base speed: 40 ft
Special: Darkvision, spell-like abilities (charm person & sleep 1/day), +1 natural armor
Half-orc Ftr6:
Abilities: +2 Str, -2 Int, -2 Cha (+1 pt at 4th lvl)
BAB: +6/1
Hit points: 10 + 5d6 + (6 x Con)
Feats: 7
Skill points: (2 + Int) x 9
Base speed: 30 ft
Special abilities: Darkvision, orc blood
Ogre Mage6:
Abilities: +4 Str, +4 Cha, +2 Con, +2 Wis, +2 Int
BAB: +2
Hit points: 8 + 2d8 + (Con x 3)
Feats: 2
Skill points: (2 + Int) x 6
Base speed: 40 ft, fly 40 ft. (good)
Special abilities: Darkvision, spell-like abilities (charm person, sleep & gaseous form 1/day; darkness and invisibility 3/day), +3 natural armor, regeneration 1
The ogre mage is rapidly going to become much weaker in a fight, and will have to rely on the special abilities and esp. the regeneration to keep it alive. Still, it looks like a fair trade.