I could be wrong because I haven't played the game myself, but the general vibes I'm getting from Mario Kart World is that even though it's not bad, it's just sloppy or baffling in some regards.
For example, why couldn't unlocking costumes be tied to, say, missions in the open world like a normal video game? And why is unlocking the meme characters tied to a roulette?
And that's sort of the big thing, wouldn't the open world feel extremely undercooked because there's nothing substantial to earn from it? Isn't that kind of the whole point?