The point being made is that it's a relative to others metric and so you can't use it to make an absolute ranking.
There are going to be team compositions that didn't win an NBA championship that are stronger than ones that did win a team composition simply because at the time the competition was stronger and so they weren't the best. So, if you use #ofChampionships to generate a ranking of all team compositions there's going to be a lot of debate that the teams aren't actually ranked by strength since some of the teams that racked up championships did so when other teams sucked (I know less about NBA but for NHL's original 6 this becomes the case, the competition was so weak that some people didn't know they were drafted because it wasn't something you cared about).
To get back to the original point, your ELO rating is in relative to your peers. The idea is that for a given point differential you have a x% chance of beating them. So the point being made is that you can't use ELO to compare anything besides two players who can physically can play each other as taking a playing in the past with n elo and having them play a current player with n elo won't match the x% chance.
To counter some of the other points (bowling and the mile). These are precise rankings not relative. If somebody runs a 4min mile in the past you can expect them to run a 4min mile in the future. This doesn't mean that they'll win the same %of races though as they did which is what elo is more about. Same thing with bowling, if somebody constantly bowled a 280 in the past you can expect them (ignoring lane/oil changes) to bowl 280 in the future but if the competition now bowls a 290 that player is going to suck instead of being a legend. So the bowler of the past may have had a very high ELO but now when taken into the future will (after many losses) have a lower ELO despite having the same peformance.
I don't think your comment is in conflict with the other's points, but Magnus Carlsen seems to be arguing that he wants to be the .9th best basketball player in the world rather than the 1st best basketball player in the world.
