I haven't made such a claim (here "better" would be solely in terms of emissions). What was implied was that the delta of the emissions from switching from beef to chicken/fish is (far) larger than the delta from switching from them to veganism (it's important to note that per grams of protein, dairy is comparable in emmissions to non-beef meats - so really veganism (or veganism + eggs) is required).
Also, this claim "we know that eating animals is not required to be healthy at any stage of life" is most likely false at the margin.