I’m in full agreement with you - all this approach does is to create bottlenecks by relying on the finite hours available by a single resource - and to your point, more often than not it breeds marginal quality in each of those disciplines.
But the larger picture seems to be this; our capitalistic approach to everything has minimized the value of our human resources to nothing more than an item on that BOM, and the profit machine can live with marginal talent as long as the product satisfies the masses, because the profit machine can’t feel, touch or discern the details. 