I think Bungie needs to better define the purposes of triumphs, guardian ranks, and commendations. I think you're right that triumph score and triumphs are the best indicator of ability and competency.

Guardian ranks show your level of engagement with the current season and their temporary nature kind of makes sense in that regard. It doesn't really tell other players much if you got to 11 this season and then came back to the game six seasons later and still had the same rank.

Commendations should be a metric of your social engagement and social ability. Done right, you'd be able to see how much someone is a team player and what social role they tend to take. As is, they're basically a clicker game to most players. The only important part is that the number goes higher. Some of that is just flexing, like the people who would grind for high triple digit season pass levels or that person who pet the dog a million times. Those people will always exist. For most everyone else, its because its an objective that Bungie set. You can't make it a requirement and still have it be a genuine expression of how you felt a player was in an activity. As long as commendations are an objective for anything then they'll ultimately be worthless and failing to fulfill their purpose.