If long term , broad participation studies with rigorously reproducible methods came to the conclusion that a vegan diet is a viable option then i would be open to switching.
The issue isn't which food is the most nutritious, it's that the evidence available in general doesn't yet support a conclusion on mid to long term viability.
You could have a team of world class nutritionist vets custom make you the best mixture and you would still have the same issue.
As i specifically said, this doesn't address the actual issue.
In case i haven't been clear, the current state of nutritional science on this matter has no consensus on mid to long term outcomes.
So taking the all of the experts in the world and creating the pinnacle of vegan pet nutrition will still garner a best guess, because, and i'm going to bold this part on a separate line:
THERE IS NO WAY TO TELL WITHOUT DOING THE ACTUAL WORK
It is potentially being done now, great, wishful thinking and anecdotal results are not a replacement for actual study.
Outstanding, and when they've provided repeatable results from long term studies with quality methodology and reasonable sample sizes that will make a big difference.
Until then it's a gamble with potentially life altering consequences (for the animals i mean)
Each to their own, your own subjective comfort doesn't prove validity, neither does my subjective discomfort prove a lack of it.
For you the risk might be worth it, but to pretend there is no risk is delusional.