9:54 at 103kts compared to 10.00 at 102kts. 6secs and 1kt.
On the day in the air you wouldn't notice the difference.
Unnecessary accuracy for an environment in which too many factors are not able to be measured with great precision.
Going for such accuracy using precision instruments in the pre-flight plan is wasted effort because you are guessing the wind vector. A 5kt, 10 deg error in the wind vector will knock all that accuracy for six, especially at the six second level.
Once I've got the wind vector, that's when I start sharpening on my eta's.
MDR is fine for unplanned diversions. So presumably it won't hurt to use it for planned diversions. That's the way I see it, the whole route becomes a series of planned diversions.
As to the nugatory effort involved with the factors and the mental arithmetic of 60, there is little to learn, and you only have to learn the ones that cover the speeds within 35kts+ and 35kts- of the cruise speed of your aircraft. The factors make the mental arithmetic easier. That's what they're there for. True, they are less accurate than the whizz-wheel but the differences in practice are barely discernible.
On my last navex to the the West of Scotland and the Inner Hebrides, the rate of change in weather meant, that to stay VFR and avoid high ground, going anywhere was a series of diversions. If the MDR is good enough for 1 unplanned diversion then why isn't it good enough for 4 or five planned diversions in series?