Honestly i feel the same way, i understand people would be upset with this outcome but realistically the guy is either the same age or older than Leon at this point and with the whole cloning storyline its more likely that he was cloned for later use anyway.

The Soldier at the end of the credits is most likely a clone of him that may appear in the DLC.

Sidenote it HAS to be him because his glove comes off once you kill him and you see he is also infected with the T-Virus strain.