Fighters can rip, ints can't. Fighters can kill caps, bombers, and bases. Ints can kill bombers, but run into trouble with caps and cant touch bases. Fighters have a very flexible weapons loadout and they have better anti-base missiles at the sup center. Also, to stage a forward attack with sups you need 2 tele receivers.
Fighters are adaptive.
They can strike in multiple places at once. They are adapted for prolonged combat situations and have a higher speed than the int. The int may be king of the hill, but a fighter can flank them. To use your speed advantage, tell a group of fighters to hit one place. When the ints respond, take the other force and hit in a second place.