Villager killing tower trade (the math)

Was just watching some gameplay and I was thinking about how in Feudal villagers are usually the best counter to towers. And I was thinking about how that works into their lack of gathering. And since I'm high on Adderall I did some math:

125 stone - 348 seconds of gather time; 290 seconds w/ koreans

50 wood - 128 seconds of gather time, 112 w/ celts

Build time - 80 seconds of build time, 56 w/ spanish

Tower HP: 1020, losing 11 HP per hit from a villager, hitting once every two seconds = 185 seconds

So 498-556 seconds of villager worktime to put up a tower, 185 seconds to take it out.

So for a tower to be cost effective you need to delay villagers a total of 313-371 seconds of worktime in addition to at least one vill taking it out.