I agree that people like the enclave should have been more resiliant and more like the lone wanderer..
however..
less than 100 years ago people were shorter, had a shorter life expectancy and were generally riddled with more health problems-many of which can be attributed to a poor diet..
Given that the LW was not only living in but raised in a vault, i would beg to say he had better nutrition through rad free vitamin fortified foods and better hygene with more regular medical check ups than your average wastelander, which would make him almost superhuman in comparison to your average wastelander..
Yes and no. Don't confuse a healthy body with being able to withstand trauma better. A baseball bat swung by almost any advlt will break the shin of another advlt (assuming a stationary target for the sake of reference), whether the victim is healthy or diseased. Likewise a bullet to the gut is still a bullet to the gut. It doesn't make any more or less damage between a sick and healthy individual as it strikes.
However, if the victim survives, then yes, a healthy person would have a much better chance to recover and would also recover faster.
In terms of game mechanics that would equate to much of a difference in HP in my eyes. If a wastelander has 100 HP, the LW and Enclave people would have 120-130 at most, not more.
However, the vault dwellers and enclave people would recover faster from diseases, addiction and damage, while the damage itself is, say, 40 across the board for everyone.
There would not be a difference of 450 HP vs 120 HP. That I consider superhuman; something for super mutants, deathclaws and such.