Not sure if having the same–or similar–powers as the one you pilot being easier to control/discover is a strict rule when it comes to using the powers of the individual being possessed, but it has been discussed previously when it was asked about. Less tangentially, I mean to say someone once asked about the ease with which the main character (or anyone with that sort of ability I suppose) might be able to use the powers of someone they have control over.
Sidestep also thought about it in the first part of book one when they try speaking to Herald through Lady Argent to get him to let his guard down.
“Fine motor skills”–as the mc put it–require the target being possessed to be closer to consciousness so that there is minimal notice anything like a possession was taking place. With Argent, they couldn’t risk letting her have that much mental freedom, because it seemed to have been taxing just to keep control over an unfamiliar body from that range.
In the case of the puppet? Something is happening behind the scenes with them whether the mc notices as much per play-through or not.