I believe having further in place is a good idea, but the academically stronger math students, who show very high capability in year 10 math, or have plans to do Specialist in year 12/ or co currently with further shouldn't be allowed.
For someone who just needs to do further to get into the course they want, I don't really see the difference if there are a bunch of stronger students competing against each other at the top end. I can't imagine a course requiring a 45+ score in further, so there's really no need to stop stronger students from "taking" all of the high scores, since no one really needs them. About 16000 kids get a 30+ score every year, and such a score should be sufficient for most purposes.
It's not like anyone's life was profoundly ruined by not getting a 45+ score in further (although I'd be happy to take that back if I see a counterexample). Might as well let the spec kids have their fun.
That said, I don't think doing further is a great idea if you're good at maths, but that's another story.