Ermmmmm, BEagle, can I ask you what you think mental ded reckoning actually is?
You seem unaware that it involves taking into account wind to correct for drift and to calculate an approximate groundspeed or head/tailwind component, using that for calculating expected time at certain points (as, it seems, does one service pilot you know, but you don't say how long it has been since he flew slow aircraft). As far as this goes it has exactly the same purpose as the use of a Dalton computer/circular slide rule. The only difference is that it is slightly less precise, but since the precision is beyond that either of wind forecasting or flying headings in a light aircraft that is, in my experience, completely immaterial. It seems you don't know or don't trust MDR techniques, so what are you teaching your students?
I was using these techniques to navigate a Squirrel at 100 kts or 60 kts, down to 200 feet, by the way, and still use them when I navigate myself. They work even at 1 nm/minute TAS. They work extremely well.
BTW my comment on not using Daltons in the air related to diversion nav, not correcting a pre-planned route. You need some MDR technique for planning a route while airborne.