Your example doesn't match the business ask above it, in my opinion, given that in your example you are both assigning users a skill (skills-based routing) and then assigning those users to a queue (queue routing) based on the same skill being assigned. The example implies the redundant overlapping of two different forms of routing intended to effectively reach the same outcome, but that each achieves the outcome based on differing system architecture. The business ask implies the use of queue routing, while the example implies the use of skills-based routing and queue routing.
Skills-based routing: one user - many skills - can do many types of work items
Queue routing: one queue(many users) - one skill - can do a lot of the same type of work item
Skills-based routing fundamentally accomplishes the same functional outcome as assigning users with a specific skill to a queue, making the queue assignment redundant (unnecessary). Although the users with a specific skill aren't in a queue or public group, specific work items related to that skill can only be routed to users having that skill. Work items can be transferred to another skill if they require a different skill set than originally expected.
With queue routing, you can only assign a work item to a single queue containing the users capable of performing a single required skill. If the work item requires a different skill then it must be reassigned to another queue.
With skills-based routing, a user can be assigned multiple skills and handle multiple different work items. To accomplish the exact same thing with queue routing, that same user would have to be assigned to a separate queue for each skill being used to effectively do the same work. Skills-based routing makes more sense when a single work item typically requires a specific combination of skills to be resolved. Queue routing becomes significantly more difficult to manage (maintain) when queues attempt to group users by multiple different skills. Queue routing is usually best in situations where there is a low variance between work item types, but the volume of work items over a specific amount of time requires a lot more users to complete.
Typically, the decision becomes clearer when you evaluate the number of products in relation to the number of skills users must possess to accomplish a given number of work items within a specific amount of time.
Trying to use both forms of routing at the same time theoretically exponentiates solution complexity, system resources, and maintenance costs.
Review the following two links: