> Like what does it mean to be good at weight lifting? And that for some reason being good at weight lifting is a good proxy for being a good bouncer or construction worker?
being a good weight lifter, means you can lift heavier weights then a less-good weight lifter. Whether this is a proxy for anything isn't relevant, because it's a purely contrived example. There are clearly jobs where physical strength (among other things) is important, and given the context of this example, there is no guarantee that a more complicated model evens out the differences.
The point of the example is, basically "there are some things which might discriminate strongly on the basis on physical traits, which might end up correlating with race/sex etc" - ask for a better model by all means, but there is no guarantee the perfect model will never correlate strongly with some political demographic, and hence be controversial.