What is the incremental OpEx/SG&A after a new subscriber connects? Assuming this is just broadband, and not video, it should be very low. So, incremental operating margin, which is probably the best way to assess incremental new build CapEx, is likely much higher than 20%. Also, 60% gross margin on broadband seems low. Tucows claims much higher. See slide 25: https://ir.tucows.com/wp-content/uploads/2023-Q3-TCX-results-investor-deck.pdf Put those two things together and you'll get much higher (claimed) margins. See slide 26.
I do want to note that I've never been able to reconcile that slide (which they've long had in their presentations) with the segment numbers. The CapEx/passing in the segment financials always seems higher than what they put on that slide. [The slide is showing cost per passing, not cost per subscriber, and doesn't include the cost of the drop to the house of a new subscriber.]
I also agree with you that there are other costs besides CapEx that must be incurred to get the system to steady state/50% penetration (marketing, etc.) so the EBITDA losses should be included, not just the CapEx, when looking at returns on capital.