Not against some kind of social metric then?

What social metric in particular? Also, for better or worse, social metrics are easily gamed. While a basket of goods can also be gamed, it's easier to see what's going on and to explain it to people, since it's composed of concrete goods. Also, a basket of goods can be expanded if we want to increase the baseline as living standards in society improve, which we do - a smartphone should now be part of that basket, even though they barely existed 20 years ago.

What is a social metric?

If the poverty hinders them too much in pursuing opportunities in education or work, for instance. Something like that. Something to keep an eye out for once the million kids who can't stay warm, dry, clothed and fed are taken care of.

I’m happy to just look at real median income quantiles. I don’t need it to be tied to an evocative word like ‘poverty’, I think there is still real work to be done to improve the lives of people who are in lower income brackets even if they aren’t in a situation similar to what people imagine when they think of ‘poverty.’