OK, I think I've finally figured this game out. A lot of people will look at the structure and go "PAY TO WIN!", but what they won't realize is that it's P2W in a way they don't even realize.
First off, getting first place in this game is not particularly difficult. I'm seven cups in and I've had little trouble taking the gold even on 150cc nearly every time. Getting first also ultimately means nothing in the grand scheme of things, there's no ranking system for winning races like in MK8D. What you actually want to do is get five gold stars on every race, because that's how you earn gifts. More characters and parts, more premium currency, and if you get the max amount of stars, you even get the special character and kart parts from the current tour's banner. Getting five stars can only be done by getting enough points in the race. Points are determined by your loadout, your placement, and what you actually do in the race.
So you have the loadout, which is determined by the sum of the base power of your character, kart, and glider at the start of the race. This can be enhanced by using them in races to slowly gain XP, or using tickets on them to get lots of XP at once. Then you have the placement bonus, which tops out when you reach first place. This number seems to increase slightly with every race you play - I've been doing 150cc races and the bonus for getting first started out at 2500, but has continually risen and is currently at 2627. Lastly you have the points for doing actions, and this is where the meat of your points come from. You get these from hitting dash panels, doing jump boosts, using mini-turbos, hitting players with items, etc.
This combined with the fact that getting first place is easy means that you do not want to play this like your average Mario Kart. Sitting in first holding a banana behind you is not helpful. What you want to be doing is hitting as many players with items as you can while doing as many mini-turbos as you can, along with using course-specific gimmicks like dash panels and jump boosts. This inherently gives a massive advantage to characters that can hold three items - not because it's easier to win, but because you can get way more points from hitting other players with all those extra items. I doubt it's even possible to get a five-star rank on certain courses without using a character who can spam lots of items. You also want good item luck from your kart parts so you'll get things that you can throw at people and not just measly coins that give you hardly any points at all.
So there's the big secret folks. It's not truly traditional Mario Kart, it's a secret score-attack game.