I'm fed up with Luigi's twee underdog bullshit. Any of the games that bother to give him characterisation have illustrated he's a petty, shit-talking jerk. In Paper Mario he's shown to be two-faced, jealous, and lazy. In Paper Mario 2, they make him more pro-active, and he bigs himself up whenever you see him, but talking to his partners re-contextualises his account of the events, often correcting his straight-up lies. In Mario & Luigi they repeatedly show off his laziness, cowardice and general buffoonery. Partners in Time even explicitly rates the fabric of his character, and says Luigi is unworthy. Heck, Luigi's own game series is about being afraid and falling for scams that even your gran wouldn't buy.
If we needed any more proof, the alt-universe Luigis are all horrible people too. Ingo from Ocarina of Time is a back-stabbing opportunist who made a deal with Ganondorf as soon as the chance presented itself. Then you have Louie from the Pikmin series, the piece of shit thief who has no qualms to sentence others to death through his selfish actions.
It's thematically fitting the Year of Luigi was one of Nintendo's worst years, because Luigi is the worst himself.