Is AES ECB mode with salt and frame counter still comparatively weak?
The point of producing different ciphertexts for the same plaintext is so that an attacker, given two identical ciphertexts, could not conclude that the plaintexts must be the same. This is indeed a weakness, but is not the main problem of ECB, which is that each block is encrypted completely independently, leaking huge amounts of information about the plaintext to even a passive observer.
Your strategy does not help with that, as the attacker could simply ignore all the ECB blocks belonging to the counter and salt and simply pick out blocks belonging to the messages, and we're back to standard ECB.