That is true gunblades... But when VIII odin came in it could save your life(if you picked a fight against something you weren't ready for), for two reasons A) he doesn't miss B) He comes at the start of battle meaning you don't have to wait for a summoner(or someone with GF summon) to summon him.

B, is my favorite reason... more often then not, if I lose it will be because I am slower then the enemy... meaning a normal summon probably wouldn't help much.