ROCE vs Cash Yields - Which is a truer measure of business efficiency?

That is the nature of Capex. It’s exactly like investing. It is giving up money now to earn more money in the future. So if you measure returns at the time you gave up money and at the time you are getting most of it back, the results will be very different. Looking at a single year’s RoCE or any return figure would be misleading.

Yes, so then that would be a terrible Capex which didn’t produce anything for 4 years. That one Capex you should not have done at all. Of course, I’m saying this generally but it ultimately depends on the sum of PV of ALL cash flows produced from that specific Capex.

Yes, and that disconnect is because you are using a Capex that is capable of producing cash flows for many years in the future, but only considering the cash flow of a single year to measure returns.

Usually a large Capex happens once in 7 or 10 years. That is the only time returns will get distorted. Otherwise over time, even measuring a single year’s RoCE / returns should not be a problem. You may read this document written by Varadha ji on similar lines: