No sure why you were down-voted, but it probably has something to do with connotation. I agree though -- library maturity, tooling maturity are also very important factors when it comes to productivity. A steep learning curve, however, probably has less to do with productivity and more to do with adoption, which I think is what the parent was trying to get across.

But, of course, adoption rate can indirectly impact library and tooling maturity. :)