Counter-example: pay on commission. Salespeople are "directly compared", but are not doing exactly the same work. Still, the work they are doing is fungible—you can compute the value in dollars both of closing one big account, or ten small accounts, and compare those.

This is essentially how a very small subset of IT people get paid, as well: vulnerability researchers, who make a living off of bug bounty programs.

Attempts have been made to expand this approach. Some FOSS projects have bounties on each issue, where whoever submits a PR for that issue (that gets merged) gets paid the bounty.

The question is how to scale this approach to work that requires more than a single person to complete. (I.e. how to distribute the "spoils" of a bounty among a team.) There are historical examples one could look at of bounty programs where the entrants were teams (e.g. the Netflix Prize), but IIRC in none of them were any of the teams really motivated by the bounty above all; rather, they were just in competition with the other teams to be the first ones to solve an eminently-achievable-but-challenging problem, and it was competition for competition's sake—essentially, a sport.