I know with certainty it’s extremely hard to do in heavily team based sports like football and basketball, because that I do pay attention to. Maybe MoBAs are closer to baseball where even though it’s a “team” sport, you actually can isolate out parts reliably enough to measure effectively, but I don’t play them to know for sure.

At least for league, I’d say it’s definitely the former. Team play and strategy is a huge component and is extremely difficult to measure. There’s no hard tracking for things like “knew when to run the opposite way so the enemy couldn’t get multiple kills” or “blocked an important spell so the carry didn’t die”. Individual skill is so closely intertwined with team results that separating out the two is only possible in the extreme cases.