> I don't buy that engineering is not also a bottleneck.

Depends. It definitely can be. When you get those people who want to spend weeks going back and forth over whether the button should be red or slightly darker red, as if they can somehow figure out the right answer from gut feeling alone, not realizing that in that time they could have tried both and learned from it, all while delivering other things of value on top, engineering has no hope of becoming the bottleneck.