Reading the ECIES algorithms (and elgamal in general), the general wisdom is to use a KDF and MAC on the shared secret before using it for encryption of ciphertext.
I suspect, however, this was because the encryption used was XOR (for data sizes that were smaller than the original).
If you're using AES GCM with a random iv, I don't see the value of the KDF on the shared secret.
For some protocols, you don't want users decrypting the ciphertext with the wrong key (chosed ciphertext attacks)... so mac'ing the key could be helpful.
But with a random IV, chosen ciphertext seems to be useless here as long as you otherwise follow standards with the shared secret and symmetric portion of the algorithm.
And with GCM, the mac portion of ECIES also seems not useful. I think, maybe, deferring to better-tested AES/GCM for the authentication seems to be the better bet.