In Rollcage the last player is a LOT faster than the leader and while it is unfair, you gotta admit it does an awesome job at keeping the group together and giving everyone a chance to finish in first place.
GRIP's ketchup is very weak (it might still be broken even), but balancing is an issue for later, when more weapons/vehicles/tracks are implemented. However, I'm fairly certain you can expect it to act more like Rollcage in the future.
Other than that, you can turn it off whenever you want. Worst case scenario multiple implementations of ketchup might be brainstormed, but offering options to select a different implementation sounds like feature creep and user confusion to me.
What do you think would be a good ketchup implementation?
I can't think of any other way other than influencing powerup chances and car speed, but I just might be too set in my ways to be able to think of a different way :p