Why vtable implementaion is not better than subtype checking implementation?

[ringabout]

It seems that the vtable implementation works great when there are 50 object 
types with 5 methods and 100 instances ref 50 object types with 5 methods and 
100 instances

vtable: `nim c -r -d:release`
    
    
    dummy value: 34803480
    time: 0.005494600000000001
    
    
    Run

the old implementation:
    
    
    dummy value: 34803480
    time: 0.0237947
    
    
    Run