Why is it only appropriate for people with heart disease / mobility issues but not for someone who is merely overweight? This feels like finger-wagging for the sake of finger-wagging.
The only way this can possibly be correct is if you think that the "correct" weight is whatever the population average happens to be which is just...wild to me.
If we assume commenter is male (a statistical likelihood), then 20% is the high end of normal, and could very safely be halved. In the less likely case that they are female, then it is right in the middle of the normal range, and could safely be reduced by 5-10% at least.
The medical definition of overweight is basically if you're some number of standard deviations above the average from whenever they ran the stats, so population average = correct weight seems like as reasonable a standard.