Can you use quota to restrict routing, or would using 'Points' be more appropriate?

Summary:

One of our business processes are reviewing the way that they plan their work and as a part of this they are setting some targets for their workload. Their workload is split into four categories and they want any given day to have a set amount of work planned as a percentage. So out of 100% of availability from the resources, they want a split like below:

Category 1 - 50%

Category 2 - 20%

Category 3 - 15%

Category 4 - 15%

We are hoping that we can using Routing to enable this and have so far done some exploration with the idea of using capacity to achieve this. Attached are some screenshots of the setup we are looking at. What we have found though is if we set the Quota % for each category then run routing, it consistently overbooks. My suspicion is that it's because the capacity/quota is only consumed once the activity is actually allocated to a resource, so routing almost doesn't 'consider' it. All of the work is Non-Scheduled until routing runs, so it's not a case of