This is obviously a troll thread, but the only things that need to be changed about commendations is what other people said, about letting us give them to people who've already left. Sometimes I see someone who does quite well (or more often, is the only one that didn't do poorly) that I'd like to commend, but they leave before I can even get the little window open. Other games that let you commend other players allow you to do it for a certain amount of time after the duty/match/etc., so it would be nice to have that here too. It would also cut down on people awkwardly standing around after, hoping to get as many as possible.
We don't need grades. It's a game, not school. If you want so badly to improve your gameplay, third-party things already exist including xivanalysis.