Brisbane

You don't need speed limits for this. Cyclists are more than capable of riding to conditions and either slowing down or going around pedestrians. Fine cyclists if they're actually riding recklessly, not if they're going at a perfectly reasonable speed given the amount and proximity of pedestrians. The fact that there have been zero incidents recorded on this bridge pretty clearly indicates it's not a problem area.

better just ban bikes(and scooters) from shared pathways

It's literally called a shared pathway. The entire point of it is to allow active transport of all forms.