> I’m always skeptical of studies like this because the group that shifts to a vegan diet might just be shifting to a healthier diet in general and therefore that might be the effect you’re seeing rather than an effect that shows veganism is better than meat eating per se.

This happens with pretty much every dieting study. In fact the population of vegans is now less healthy on average as it's become more mainstream and more junk food products are aimed at vegans.