Car arrived at the dealer just before the lockdown so no time for pdi etc. Dealership has just opened with skeleton staff and Covid precautions in place.
You seem to think the smaller battery does not have the 800V system. This is very incorrect. In regard to charging the max charge rate is 270kw/h for the larger battery and 225kw/h for the smaller battery. Both of these rates are very fast.
Yes I think it is a mistake. The 4S with the Performance Plus battery model is being treated as a separate model for residual value purposes. You will get back the extra cost in extra resale value. But your choice - you might want the less weight of the lighter smaller battery.
Looking at the prices and the spec of these 3 Taycans on the Sytner website they seem to be priced at least at list price and possibly over list.
Nothing to be concerned about here.