"Certainly in the Deuteronomic context blessing consists of more than
numerical increase: it is the general well-being in the land of a
people that keeps the commandments. So it doesn’t seem unreasonable to
read Genesis 1:28 in the same way."

It’s not unreasonable, but it’s not an interpretation that’s demanded by the text. I don’t think there’s a compelling exegetical reason in this particular case to interpret earlier events by the later, such that the Abrahamic promise restates the original "be fruitful and multiply" creational blessing while concentrating its scope on a "microcosm" within the larger created order. As discussed in Peter’s post I alluded to previously, your "microcosmic" reading denies full human status to everyone who isn’t part of the Abraham-Israel-Church microcosm. To make that ontological distinction between the incompletely human and the fully human is, I aver and document in that other post, both unbiblical and fascistic.

As you say, the Deuteronomic promise "consists of more than numerical increase." Only the numerical increase, as well as the ability to subdue the earth and to dominate the earth, is explicitly stated in the Genesis 1 blessing. It’s evident that man has increased numerically and has subdued the earth. Why not just let the Abrahamic covenant supplement rather than restate that original fulfilled blessing? I.e., everyone is fully human, but only some humans participate in the supplementary covenant of faith. righteousness, and eternal life.