DB, you are incorrect. PANS OPS make no such assertion regarding 200ft MSD prior to DH if on GP. Take a look at:
Northolt RW25 - TDZ 124, 0.55nm (3.5 deg GP) 131ft
Gloucestershire RW27 - TDZ 87ft, 0.55nm (3.5 Deg GP) 102ft
There's many more where your radalt at DH will be less than baro alt (QFE). There are a few more exotic ones where the scenario appears at greater range.
Use of Radalt in IAP design is also mentioned in 8168. Personally, I set radalt to 50ft on an IAP but that's because I'm normally calibrating the ILS and 50ft is a good point to start roll-out guidance on a Cat III.
We digress, I see where you are coming from and would support the use of the radalt bug to increase SA.