Its not that its weaker, but technically it is, why? because the person who is Controlling them, is controlling them like a puppet, and can only do the jutsu they know they can do, For eg , Kabuto just remembering he could use chibaku tensei on itachi naruto and bee, They can only perform at best of the person controlling them , Which makes them weaker than how they would perform on their own ....... ,
This however has exceptions , For eg When the edo is fighting on their own free will Ie - Madara, He knows his capabilities, and is doing the stuff, Kabuto knew nothing of what madara could do, that meteor jutsu etc, which is why he asked madara to show him his power before taking control of him