Great question! You've kind of already sussed a big part of it out, the final group rolls really decide the race, whereas the checkpoint roles really just determine the narrative flow of the race - you still progress to the next checkpoint just with some disadvantage. But there were a few other considerations as well!
Taking a Failure with Hope is the only way players can take an action, use an ability, or do a stunt (for the bingo reward cards). So already our baseline is lower than average checks.
This also builds in a reason for players to link up their rigs - as the SPEED DIE increases for everyone whos linked up by 1 per player. This also is incentive for players to want to win races and upgrade their bikes - I really like this element and wanted their to be soft progression system to the racing element. You start with a shitty rig and by tier 3 your a superstar racer rolling 3d12 while racing.
And the vibe. Because its a death race, every check point has something could actively kill the players (at least in narrative) so i wanted it to feel overwhelming a bit. A high check will make your players feel like they need to use boost, spend hope to help each other / use experiences. Their is a psychological element to it, lol.
Thank you so much for your kind words and thoughtful question! Don't hesitate to ask if you end up having any others!