Cows are extremely inefficient (2% conversion) at converting calories to meat, so putting cows on that land is also an inefficient use of that land. And land with bad yield for crops also has bad yield for cows and the grass they eat and the water they need. I don't see the proposition being made in these claims.

Cows are so inefficient that we don't need to use marginal land at all to grow food. The majority of arable land is already used for cows yet they produce a disproportionately small amount of food. Weening off cows is a good thing.

Dairy cows convert calories to milk at over 24% efficiency. And you still get the meat.