It is indeed nonsensical to have the same upper maximum speed limit (70mph) on motorways (restricted users) and dual carriageways (all-purpose roads): so simply lower that for dual carriageways rather than ban a legitimate road user due to poor driving. And visibly differentiate them from motorways to show that they are all purpose roads with slow and vulnerable road users present.
Highway code rule 225* is an admission of culpability in my opinion: ie the speed limit on an all purpose dual carriageway is too high if amber flashing lights are required on tractors yet inconsistently not on mopeds pedestrians cyclists. Perhaps the rule is actually to protect the careless driver from injury rather than the occupent of the slower (but substantial) tractor, thus placing slower vulnerable users at greater risk not less by not teaching driver a lesson via a dented 'precious'(vehicle) or removing them from the gene pool? Can the authorities not be sued for not having a 50mph limit on all dual carriageways so as not to endanger old-tractor drivers and cyclists and pedestrians and moped riders etc etc?
No one is forced to drive badly, even on a dual carriageway.
Any road can become full to capacity at some time, to ban cyclists rather deal with bad driving is, as observed above, to allow theft of road access by allowing faster vehicles to endanger legitimate slower road users unchecked then claiming they (slower users) should be banned rather than the perpetrators. Why should I give up the legitimate backup of using a road in the case of the much vaunted proposed alternative cycle route being blocked/slippy etc etc.
*
225 Vehicles with flashing amber beacons. These warn of a slow-moving or stationary vehicle (such as a Traffic Officer vehicle, salt spreader, snow plough or recovery vehicle) or abnormal loads, so approach with caution. On unrestricted dual carriageways, motor vehicles first used on or after 1 January 1947 with a maximum speed of 25 mph (40 km/h) or less (such as tractors) MUST use a flashing amber beacon (also see Rule 220 above). Law RVLR 1989, reg 17