Amazing post. I agree by 100%. Typical job posting for a web developer position looks like "It's mandatory for you to know 100 back-end frameworks and it would be good if you would know 50 front-end frameworks too". I suspect the biggest reason of this phenomenon is that companies tries to cut costs and/or they simply don't finds suitable persons with skills required, so throws every possible duty to the hands of one worker. And the bad outcomes of such approach appears very quickly.
For example - I have asked my manager why my company don't starts some project X. The reply from the manager was that X project was started in the past and it has failed. I have asked further - What solutions have you tried in a failed project X ? The reply was,- "the ONLY solution Y". After this answer I was amazed - How can one declare a project X as "failed" if there was only one solution Y tried ? It's not that hard to imagine that in IT field almost every problem has at least several solutions. So after trying N solutions you can only state that "exact N solutions don't helps to solve problem X". But maybe N+1 solution will solve that problem finally. BUT it takes only a professional in some field to actually be able to grasp and generate this N+1 solution. Jack of all trades will not be able to achieve this. As long as companies will not be able to understand this - we will swim in a deep sh*t sea as we always were.