You ask funny questions! :)
As a mechanical engineer, you would know why somebody would go to all the trouble to put a large number of fine diameters spokes on a wheel, instead of something much simpler, like being solid.
So, they would not be the same diameter as well as the same weight, especially if they were the same material. If they were, such as you had a way of making very thin solid material that would be of so little weight to match the spokes, then yes, you have made it so there is no difference.
Perfectly clear, right?
Two flywheels with the same spinning inertia force, are the same flywheel, just one more practical for a different mechanical setup then the other.