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[brimstoneSalad]

#1. In the abstract people just need nutrients, but we are biological systems and specific nutrients don't magically go from our month into our body. The source of the nutrients is important on a number of fronts, for example:

i.) The source of the nutrient can impact how the nutrient is absorbed

A matter we have adequate research on. We know roughly the differences there and can account for that in recommendations with reasonable safety margins based on the remaining uncertainty.

ii.) Nutrients come packaged with other other compounds and those compounds can have positive and/or negative impacts on human health.

Funny, because this overwhelmingly favors plant-based diets and draws into question the long-term health of consuming animal products.
Generally anti-cancer vs. carcinogenic, etc.
It's an area of ongoing research, but what we do know doesn't favor your pro-meat dogma.

iii.) Source can determine the form of nutrient present, for example, supplements are often made with synthetic versions of nutrients because
the natural form isn't stable outside of food. The synthetic versions typically have different metabolic pathways and as a result can have
differential health outcomes.

Just a bunch of fear mongering against supplements. Supplements for major nutrients are well studied and safe at small doses. Only overdosing is dangerous.

while its true that all essential nutrients (other than B-12) are found in plants there is question about whether everyone can adequately synthesis the down-stream compounds from their plant-based precursors. For example, the case of synthesis rates of long-chain omega-3 fatty acids (e.g., DHA) from the short-chain versions contained in plants (ALA).

It's not hard to find plant based doctors and dietitians recommending vegans take DHA.
If in doubt, there's no nutritional harm in supplementing these things (just monetary expense). Though there's no credible reason to believe we should have to unless we're in the age group otherwise recommended to do so. It really only makes sense to take a cheap multivitamin.

Now its certainly possible ( and I like very plausible) that with the appropriate knowledge you could craft individualized vegan diets that work for nearly everyone but we don't have that knowledge yet.

Professionals disagree with you, so this is yet more fear mongering.
Consensus is that well planned vegan diets are adequate and appropriate for all stages of life.

You can believe that we don't know anything about nutrition if you want, but this is nonsense along the same lines of flat-Earthers claiming we don't have enough knowledge of the shape of the Earth yet. We don't need to know the precise height and depth of every peak and valley to get the general picture.

Is veganism challenging to some people due to socioeconomic circumstances, allergies, etc? Absolutely. Is it practically impossible for some of those people? I can believe that. But it's not the nutritional knowledge we're so lacking in, it's infrastructure and public education.

Currently vegan diets are based on very general guidelines that may or may not be appropriate for most people.

Currently the average vegan diet is based on basically nothing but taking animal products off the plate, and that's going to be suitable for very few people without replacing them with other protein and nutrient sources.
If a steak and potato diet becomes a potato diet, that's not necessarily an improvement contrary to the claims of high carbers.

What the uneducated public does and what they should do based on the body of current nutritional knowledge are two different things.

It's an understandable and sympathetic argument to make that people shouldn't advocate for veganism because the general public is incompetent. I disagree with that, and think instead we should try to pair the encouragement with better recommendations and better recipes, and promote more nutritious plant based replacements, but reasonable people could disagree on that point of public outreach.

Fear mongering and pseudoscience isn't sympathetic, though.

But many people report issues with vegan diets and there has been little done to understand the nature of those problems.

Not that many, which is surprising given the diets I've seen vegans following, particularly some new vegans, and the general hesitancy to take a multivitamin.
If there were credible evidence of a significant number of people struggling on a well planned vegan diet -- and not just vague personal accounts which are more likely to be rationalizations due to peer pressure but something like actual lab work -- I'd be very interested in understanding that.