I feel that anyone who advocates to stop eating meat for methane reasons is a vegetarian in disguise who latched onto global climate change to push their own agenda, having failed to dissuade meat eaters on animal rights grounds. They are doing the fight against climate change a disservice by muddying the waters. If they were serious about methane specifically (which anyone concerned about GHG should be, to within (x*25)% of its contribution), they would be dedicating 10 times more of their time in researching some kind of pill to give the cows to stop them from making methane - a much more feasible outcome. But doing so does not synergize with their animal welfare goals.
That’s about efficient use of land space, not related to GHG specifically other than tangentially regarding deforestation. Also elsewhere in this thread cattle was accused of being inefficient precisely because they sit in warehouses and eat cereals instead of grass. If cattle can roam pastures and eat grass, that’s an equivalent amount of cereals that did not need to be grown, farm machinery that did not need to run (on fossil fuels) to grow them, and a good amount of land possibly too hilly and rugged for any use otherwise put to productive human use through grazing.