But that assumption is incorrect. Adventurers, by definition, are weird. You are going to see massive over-representation of the unusual ends of the bell curve--both the weird because they hyper-exemplify their physiology, and the weird because they radically differ from it. Ordinary selective pressure (adventurers with poor stats do not survive as long as ones with good stats) and self-selection pressures (adventurers with low Strength are rarely going to pursue a career path as a Barbarian and other similar patterns) will provide a strong filter. Further, folk who fit in perfectly with their society's expectations aren't likely to gallivant off as adventurers, risking life and limb when they could pursue a much
safer vocation.
We are, necessarily, going to be comparing
weird dwarves to
weird non-dwarves, because they're adventurers. And the weird dwarf adventurers who choose to become bookish Wizards
aren't going to be the ones who exemplify typical dwarf strengths, are they?
It's not a matter of "you stopped being a dwarf when you became an adventurer." It's "adventurers are already a weird, self-selected group that doesn't conform to social and, frequently, characteristic norms." Dwarves that already didn't fit in are the ones most likely to become adventurers in the first place. By your phrasing, it is "dwarves who decide to stop being dwarves" that are particularly likely to become adventurers. (There will, of course, also be at least partially-stereotypical dwarves who become adventurers, but it's pretty much inarguable that wandering adventuresome dwarves are deviating from the stereotypical dwarven culture's values, seeing as they're leaving their family and clan behind and usually living
above ground most of the time!)
This is, of course, completely separate from the two excellent arguments from
@Remathilis (why are ASIs tied to advancing
class level if they are always inherent and never obtained through life experience and training? Surely your arguments indicate those should be removed too, and that's
not going to happen) and
@Aldarc (dwarves
already are inherently tougher and hardier, as they have higher HP and a resistance to poisons and poison damage--why are ability scores
also needed when these features exist?)