I don't see why that implies we shouldn't take it seriously. The world #1 didn't want to play, so we got a great match between the world #2 and #3 with some very interesting and complex games. Do you also think that Karpov shouldn't have been taken seriously as world champion?
Ding is in fact the sole player that can make this not statement not true, as he is a candidate with a known positive score against Magnus. A couple WCCs ago Magnus said Ding was the only player that he wasn't sure he could win against -- but that he wouldn't make it, after a poor showing in the candidates at the time.
Anyways, I don't know who would win in a Carlsen - Ding WCC. Nobody does. If the game statistics are to be believed, then Ding would.
He first voiced his discontent with the format around 13-15 years ago (he was #1 player by elo rating, but not yet the world champion), even skipping a cycle or two as protest. Afterward, he participated anyway and hold the title in fairly dominating fashion 10 years straight.
Maybe we should take his words at face value and that he really is fed up with the thing.
Considering how much happier he seems since he decided to forgo defending the title yeah, good chance he just doesn't want it or care about it anymore.
IMO good for him. He won it all and now he is doing new things with his life.