Some suggestions.

Agreed on all parts. I, too, love this franchise and am glad to see it back but it seems like the gameplay loop is rather repetitive. I hope down the line they add more activities to do in the game so we don't have to simply rely on challenges to progress. As for your 1st point here's how I would try to explain it to the devs - imagine if you were a skater and you hit a sick line on a spot, you wouldn't go back 2 days later to hit it again, and then again and again with little to no variation. Idk how easy it would be implement player-made challenges since it all needs to be coded in I'm guessing. Having the skate council team make some challenges could be cool, or pro skaters. A neat little cutscene or a video that plays to show you how it's done and then we gotta do it ourselves would add so much immersion.