And yet most of that doesn't matter, because you almost always have local resolvers that do cache properly.

Your average consumer router is a pile of garbage that barely works.

I'll admit I don't have the stats in front of me, but I'd bet over half of them either don't attempt caching at all or do a horrible job at it.

Of course, your upstream resolver (hopefully) does do some caching, but as most of the latency is getting to this resolver in the first place that doesn't really matter.

Consumer router doesn't seem to need to given that they typically have such low client counts. Your computer is doing caching, so there's not much benefit for your home router to also do caching.

The latency to most ISP cores is low ms range. You really should just stop digging.

Maybe you live in a country where ISP routers are well designed and low latency, but where I live in the US the primary latency in DNS lookup is almost always the round trip to the horribly configured and slow ISP DNS.