A few more points:
cows mostly eat grain because we stuff them full of grains to fatten them up (just like we're doing to ourselves). They're perfectly fine eating natural growing grasses that we can't eat.
Right now grass-fed cows are only 4% of the market, so we are, in fact, growing massive amounts of grain on arable land, with all the issues you brought up, in order to feed cows. From Cattle Daily, "over 60% of cropland in the US is used to produce livestock feed", or 200 million acres. Also, "hay production occupies around 60 million acres of US cropland annually", so the hay is grown on cropland and fed to the cows; they're not necessarily grazing non-arable pasture. From that same article, "In the Amazon rainforest alone, over 70% of deforested land is used as pasture for cattle ranching".
So again, much or most of that 200 million acres currently used to grow food (mostly corn) for livestock could be used to grow plants to feed people directly. This is not a hypothetical "switch" requiring additional land or water use.
You only need to raise one cow per person per year. Small families do manage that. It's significantly less work as nature does most of the work for you and is being accomplished all over the world.
This does not scale: How many Americans have enough land available to raise (grass-fed, grazing) cows, even if they wanted to? And what would happen if everyone tried doing that?
the USA EPA states our animal industry contributes 3-4% to our climate impact.
Does that estimate take into account deforestation, transportation, refrigeration, everything it takes to grow feed, etc, or just methane emissions? I.e. does that include the impact of the 200 million acres used to feed livestock?
You can't do the same with vegetables nor grains and they aren't renewable resources.
Plants can be composted and help regenerate the soil. And of course they are renewable because you can sow the seeds from one plant to grow new ones.
You can prevent/resolve most cases of diabetes though low carb diets.
If you're suggesting that vegans/vegetarians have higher rates of type 2 diabetes, the opposite is true: there is an "inverse association".