Its just a MK2, not an "I win" button.
And, its not just an additional slot, you also get another bonus; varying on bot.
The idea being, that if you run up against a MK II, you don't have to just run for your life, they will have an advantage but they are not indestrucable. And from the other side, just because your in an MK II doesn't mean you can defeat anything infront of you.
If your trying to say that its not worth 10x the NIC to upgrade to a MK II for a few slots, that is a valid. But some players, who have thier skills to 8 or 9, and are looking at 28+ days to pick up 1% more damage, may not care about cost.
And for beta groups, outfitting with MK II's could give them the edge, and cost is less a factor then production time.
Edit: Sequar vs Lithus is the perfect example. If you don't have a specific requirement for hauling more than 80U's, there's no need to spend 10Million on a lithus when a 500k Sequar will do the job. Its also not worth getting a MK II to test out some fits, but if you have something that you can't do with the MK, than your only choice is to get a MK II.