Im playing since the start of the game,so i havent see that other summons have other stats .
I checked the stats of all the summons:
choco-mog,shiva ,ifrit,ramuh,titan,odin,leviathan,bahamut
(+50 str, vit,mag,def mag) (With 4 summons im God xD)
kjata,Alexander,Phoenix,Neo-Bahamut,Hades, Typhon
(-30 str, vit,mag,def mag)
ZERO,KOTR
(-15 str,mag
-25% HP,PM)