"It seems to me that there is a material distinction, as drawn in the authorities, between a claim for diminution in value of the asset as reflected in the reasonable costs of repair payable by the individual claimant on the one hand and a claim for loss of use of the vehicle as reflected in a claim for a replacement car on the other."

As he rightly says, what is recoverable regardless is the diminution in value, and that is reflected in the reasonable costs of repair. If you want to claim special damages for consequential losses (eg hiring a replacement car) that has to be proven. A restatment of the rule in Dimond v Lovell and Burdis v Livsey. Personally, I would express that as the difference between damages reflecting iniuria and damnum.

Entirely orthodox and correct.

Rob