In the arcade, after you select your character, select mirror mode. Notice that the cup and course selection has 150cc mirror on the top right corner. By choosing normal mode contains 100cc. Comparing to 100cc that has shown in yellow. 150cc mirror was shown in purple that you selecting it. Imagine that you drive 150cc mirror is driving you even faster. In 100cc normal, it's slower than 150cc mirror. Medium, hard, and very difficult course such as Mario, Don-chan, Pacman, Donkey Kong, Bowser jr, and Bowser cup takes lots of handeling for high speeds without going off course. An easy course such as toad cup you choose, making it more easier to drive.

you have to play your account up to 150cc, then you get one chance to do an all cups run before you have to return to title screen after every race. Arcade Mario Kart is a pain to run but this game takes it to a new level of inconvenience. IDK if this answers your question;

TLDR ; dont run this game

Regards, Boston