I think that interpretation's along the right lines alice, but I can't reconcile the new Death with the Auditors 'grey' mindset because, by the definition of their nature they're not
theatrical or individual/diverse or in fact 'expressionist' in any way.
The shopping mall concept does suit them certainly, as I equate them (and the clue really is in the name Auditor
) with accountancy and tick boxes and common denominators and standardisation
rather than creativity and diversity and general 'messiness' which is what Life writ large is all about - it's that concept that's utterly alien to them and what Bill Doors tries to embrace. In a way the new Death's nothing to do with the Auditors and all about what 'Life' would create to fill the void that Bill Door's demise would leave. I think it's actually said somewhere that this will come from the living and why they get a really 'deathy' Death, because it's filling the niche for the human interpretation of Death (with skeletal horses and no mercy) as well as the Death of Rats, Fleas, Gerbils, and everything else to take on the amalgamated and generalist role Discworld Death is being forced to vacate? Certainly he's the epitome of the cycle of Life and Death and is capable of evolving as well (as he's tried skeleton horses and fiery steeds and realised that a normal horse is far and away the best option for comfort and avoiding pyromania
) and actually takes an interest and pride in his work because he's responsive and curious. The new Death as a concept perhaps is what the Auditors want in the way of efficiency with no real substance or empathy, but in reality it's their antithesis because it's so into 'glamourous' theatrics almost.
Writing this too I think on this and subsequent outings the Auditors also are gradually becoming infected with a tendency to dispersal and individualism as seen in Thief of Time, possibly because of the magical field on Discworld - really in their original form they're creatures more suited to Roundworld, which is why Discworld ticks them off so much?