Seems like you should switch body/powers, since Glads body is probably more durable than SS and Surfer's powers are clearly >>> Glads. Then I feel like you have yourself a fight, because you'd get Doom's magic and tech combined with Surfer's powers and Glads' strength/durability.
I'm pretty sure he did it to utilize Surfer's ability to amp himself to untold degree (plus, Surfer's speed, strength, and durability), and he added Doom's, because Doom has a great knack for things like this (able to figure things out easily). Plus, who has more confidence than Doom (which is Gladiator's power - to make himself more powerful with more confidence)?
I guess I should have clarified that I'm using the "classic" amalgam system where the amalgam technically has ALL of his components powers, but what powers he can use effectively is determined by the "mind" character.
See I put Glads as the "Powers" character because Glads powers are psionic in nature rather than physical, so they should carry over and directly stack with Surfer's already impressive physical attributes.