Ethic is the leading reason for the vegan lifestyle [0]. It's also well known [1] that a plant-based diet is effective with colorectal cancer (+9%):

> The random-effects model demonstrated a significant inverse association between plant-based dietary patterns and CRC risk (hazard ratio [HR], 0.91 [95% CI, 0.85–0.97])

But as you guessed it varies between healthy and un-heatly diets:

> This protective association was strengthened when the definition of plant based patterns specifically emphasized the inclusion of healthy plant foods

However those un-healty foods are not restricted to plant-based meal (evidence: any supermarket shelf or snack restaurant), and lentils, tofu or seeds are as much -or more- likely to be found in a long term vegan dish than an impossible burger. As you noted it's "Not just vegan brands, but overall". For the mayo I recommend tahini instead (way more tasty) or just olive oil but if you really need it:

  - ~2/3 sunflower oil
  - ~1/3 soy milk (with no additive ;-) )
  - a bit of citrus juice
  - a pinch of salt
  
  -> Blend high speed to emulsify
  -> For a thicker texture you may use some silken tofu

0 https://www.statista.com/statistics/1264382/top-motivations-...

1 https://www.sciencedirect.com/science/article/pii/S1091255X2...