OKW is all about the aggressive start. The Kuble allows them to grab alot of ground very fast and not sacrifice early game firepower
It absolutely sacrifices firepower. Apart from its poor damage (which I can concede is a difference of opinion) any damage it takes is not only sacrificing its firepower, but the surmpioneer's too. Every second it spends repairing it (which was double hit during the patch that nerfed their repair speed as well as increasing kubel HP and lowering Armour), is a second its not using its early superiority to push.
As you said, OKW is about an aggressive start, cant do that if your surmpioneer is buzy repairing.
On a tangent, the only late game role it has is building it and throwing it away to decap a VP or cutoff.