I agree that there's potential for sustainable husbandry in grasslands you cannot use otherwise. But it's very small and could not sustain today's mean consumption at all. Meat production relies heavily on farmed feed, with very low efficiency (25kg of feed for 1kg of beef). For growing that feed you need a lot of farmland which is a driving factor for the destruction of carbon sinks like the rain forest. Here in Europe for instance we are not able to produce enough feed for our animals, so we heavily import from the Americas.

Also your argument against methane emissions is not very well thought through. You could argue the same against any CO2 emissions, by arguing that at some point they will be stored by CCS again.

https://ourworldindata.org/grapher/feed-required-to-produce-...