I'm a bit puzzled, isn't the 5-series classed as an XCAR in the US? So they had them on the lot, but gave you an LCAR instead despite your booking for XCAR?
Or those 5-series weren't ready for rental yet, e.g. fresh deliveries? Else I'd been quite adamant to get one - this downgrading nonsense is getting worse in my book and then often one has to argue about a price reduction. Guess we need to be grateful to get a car at all

.