If you applied your logic to DNA sequencing. The first DNA sequencing took ages and by various estimates at the time it would have taking 100+ years to fully sequence DNA. Fortunately exponential progress doesn't work that way and full DNA sequencing happened orders of magnitude sooner than those pessimistic estimates.

I see no reason to believe A.I. will be any different. But then I don't believe Moore's law is dead. We'll find other ways to extend it. Insert magic here.

http://michaelgalloy.com/wp-content/uploads/2013/06/cpu-vs-g...