Yeah the side quests for dragon cart kinda blow. More modifiers would have been good. Have yet to try time trials though. I’m mainly more annoyed about the jump to 300 stars for the last rank with the baito hero stuff. Still otherwise minor flaws in a fantastic gameDragon Kart is great fun for me in time trial mode, most of my time is spent in that mode, shaving a few seconds off each time. The races are definitely way too easy, and I don't like the fog based side story races at all because its really hard to gauge drifting when I can't see the road ahead of me until its almost too late.
The Byte Hero stuff is best left in the background, I've done 80%+ of each mainly just by playing the rest of the game. I find the tick off almost all of it as I go, aside from a few of the rescue fights against enemies that seem to spawn rarely. Thankfully its basically optional so unless your a completionist like me there's no need to tackle most of it.