What a deficiency-versus-effect matrix is trying to capture
Ranking vitamins and minerals on a single chart forces three distinct questions into one view: how common is deficiency for this nutrient, how large is the measured effect of supplementing, and how trustworthy is the evidence behind that effect. These axes do not move together. A nutrient can be widely deficient yet show modest supplementation benefit, or rarely deficient yet show a large effect in the specific people who lack it. Reading the matrix usefully means treating each cell as conditional on population and baseline status, not as a universal recommendation.
Effect sizes for correcting a genuine deficiency are typically much larger than effects of supplementing people who are already replete. This is why blanket supplementation trials in well-nourished populations often report little benefit even for nutrients with strong deficiency effects.
Why evidence quality belongs on its own axis
Evidence quality varies enormously across micronutrients. Some claims rest on randomised controlled trials with hard endpoints, others on observational associations that are vulnerable to confounding (people with higher nutrient intake often differ in many other ways). Separating effect size from evidence quality prevents a confident-looking number from masking weak data. A large apparent effect with low-quality evidence should be read more cautiously than a smaller effect supported by robust trials.
This is general educational information, not medical advice. Whether any specific supplement is worthwhile depends on individual diet, blood levels, and health conditions; consult a qualified healthcare professional rather than acting on a comparison chart alone.