I think both solutions work hand in hand. We replace the lower quality meath with vegan alternatives. This allows meat producers to focus on higher value, grass fed products. So we still eat steak but frozen processed meat patties are replaced with plan alternatives.
This is really meat-dependent, ironically - the biggest thing we could do is cut consumption of steak and other prime cuts of beef, since ground beef is made out of what's left after those expensive, sought-after cuts are taken. I would guess that eliminating ground beef consumption doesn't really get us anywhere for the environment.
