It is important for animal advocates to be intellectually honest about the balance of the pros and cons to health from abstaining from animal products (being vegan). If they are not intellectually honest, their arguments will be discredited and discounted in the future by the general public.
Unfortunately, I think some of the popular medical doctors advocating for plant based diets, including Neal Barnard and Joel Fuhrman, have gotten a reputation for only presenting one side of the evidence. Similarly, I am not sure if the 2018 documentary Game Changers helped or damaged the arguments for plant-based diets since it was widely reviewed as insufficiently sober in its handling of a complex subject (https://www.menshealth.com/nutrition/a29067926/the-game-changers-movie-fact-check/). If I am wrong about this I would be happy to be corrected.
I have heard arguments recently that one of the most important components of healthy aging is minimizing sarcopenia, and this cannot be feasibly done without large doses of protein, including animal protein, spread out throughout the day (https://peterattiamd.com/donlayman/). These arguments are being advanced by respected academics, who are also arguing against school lunches going plant-based.
If animal advocates are going to suggest that the public abstain from consuming animal products, I believe they should address the sarcopenia point, and other similar points, directly and credibly. If this has already been done, I apologize, and would request that someone direct me to those materials. If it has not, I would like to suggest that this is a void that would be helpful to fill.
With regard to differing forms of , the article you linked notes:
Which is understating things a bit: All the minor variants will be identical after dissolving in the body -- anyhydrous creatine will become hydrated, and particle size is 0 after the creatine has dissolved. The only (minor) difference is that micronized creatine will dissolve slightly faster if you mix it with a drink, because of the smaller particle size. This can be mildly convenient, but I've never been bothered by the monohydrate being too slow to dissolve (it's almost instant for both forms).
With respect to the impacts on cognitive performance, Gwern completed an in-depth look here. Most important is the section on publication bias; the authors of these papers failed to replicate their results several times, but these failures were never published. Gwern concludes (and I agree) that creatine almost certainly doesn't affect intelligence in nonvegetarians, and has at best
The study you quote at the end about vegetarianism has a sample size in the low dozens, and I wouldn't put much stock in it. The large meta-analyses of this all find better life expectancy and health markers in vegetarians/vegans. The one important exception is B12 (for which the study you cite finds a deficiency in vegans). Luckily, th
is can easily be fixed by supplements.