Not the case with asymmetric encryption, you could encrypt with a public key and only the server's private key would be able to decrypt it. Not even the client could.
I think the person you're replying to perhaps meant that if you have total control of the hardware and the binary you can pull the value prior to being sent to the encrypt function.
Fair! In that case, yes you totally have access to the payload before its encrypted.
Asymmetric encryption is very computationally expensive - there's a reason that it's typically only feasible to use for signing a hash or as part of a key exchange to agree upon a shared symmetric key.
Envelope encryption works for that - client generates a random symmetric key, encrypts the data symmetrically, then asymmetrically encrypts just the key (which is then thrown away on the client). Both the symmetrically encrypted body and asymmetrically encrypted key are sent.
You just modify the client to leak the data before it's encrypted symmetrically. Keys don't matter at that point.