When most of the elements are no-ops/unused, I don't think we should be making any assumptions about the performance at max capacity. Contiguous iteration is cheap. The author may call it the constant work principle but I can't agree.
In the context of HFT, since the author drew inspiration from the domain, there's also the issue of now having introduced new branches into the hot path. A lot of work goes into reducing branches and priming the predictor in advance of orders actually being placed. Granted, you could potentially be avoiding branches elsewhere as a byproduct but that's probably getting into the weeds and nitpicking the examples.
In the context of HFT, since the author drew inspiration from the domain, there's also the issue of now having introduced new branches into the hot path. A lot of work goes into reducing branches and priming the predictor in advance of orders actually being placed. Granted, you could potentially be avoiding branches elsewhere as a byproduct but that's probably getting into the weeds and nitpicking the examples.