Switch / Dictionary containing multiple values with same keys
Dictionary and switch are far from the same, even in your case.

As a general guideline I use a dictionary as a lookup mechanism and a switch as flow control. 

As a lookup mechanism a switch is less efficient than a dictionary. 

Maintenance wise, adding new values to a dictionary is not changing code per se. Modifying the dictionary will not cause a change to the code calling it. And a dictionary has a built in error check - you can't have the same key twice with different values.

However the switch is very much involved in program flow control. Therefore changing the switch code is higher risk than changing dictionary content.

Finally, using a dictionary decouples your data from the code that uses it. It makes the data re-usable. And you don't have duplicate switch code everywhere the data is used.