The comparison between cars and homes is silly and we can end it here.

They are not comparable in every way, but with respect to depreciation, the reason they both depreciate is the same: They both deteriorate over time and with use. Depreciation measures the cost of that decay. The original context was specific about it referring to the deprecation aspects.

We’ve also established that a home that’s been maintained and updated should not only hold its original value, but be worth more than it cost.

I'm not sure that is established. It is established that it is technically possible for that to be true if new homes prices are rising in kind. That has definitely been the case over the past decade, or even the past few decades.

But over the long history? Traditionally, homes in good condition have only kept pace with inflation. Historically, if you bought a home for $100,000 then you should be able to sell it for $100,000 (we'll assuming inflation is zero to keep things simple) a decade later, assuming you've kept it in the same condition. Great.

But let's say you had to put $25,000 into upkeep during that decade. So your original cost was actually $125,000. You had to eat $25,000 in depreciation costs when you sold it for only $100,000. Had you done nothing, letting it rot over those 10 years, then the house would only sell for $75,000. You also had to eat $25,000 in deprecation costs. It's the same either way.

I still don’t understand what the argument is.

I didn't see an argument. What are you referring to?