AI is way too aggressive

Hi all, I'm wondering if anyone can give me any tips on how to get good at this game. The AI seems absurd and I have no clue how to beat it.

It seems like no matter what I do, it's nearly impossible to open up a real lead. In knockout tour, I sometimes have trouble getting into first at all. The AI... just keeps up, no problem. I use mushrooms and feathers for shortcuts and watch them keep pace while regularly driving the course, I use mushrooms to try to catch up and it's like they boost right away, I do a full drift and don't even eat any of the distance between us.

If I do get into first the item barrage is absolutely brutal, blue shells once every 30 seconds or so, and if I do get incredibly lucky and roll a horn for defense, it's always conveniently stolen by a boo or lightning. Red shells are a menace and it's impossible to defend against three of them back to back.

I've also seen the AI get way better items than I do when in first, like red shells or mushrooms. I've never gotten these.

Am I crazy? Because I feel like the AI simply defies the rules of the game to keep me from winning, and I feel like that isn't fun. Maybe somebody can give me some pointers.