With a lot of patience, time, and hundreds of beaten-up thugs later, not only was I able to finish the game on Hard Mode, but I successfully completed all the side missions and discovered all 440 (whew) Riddler trophies! I think the time I spent on the side missions would've been much faster if I didn't stop to beat up every low-life I saw wandering the plague-ridden streets.
For the record, both Uncharted 3 and this game were actually completed late last year, but only now have I found time to actually post a blog about it. But I'm happy to report that I've successfully done what I did with Uncharted 2 and Batman: Arkham Asylum - to play the game initially in its hardest setting and complete it. Now to begin "New Game +", where the game becomes increasingly harder and there are no counter prompts to warn you of thug attacks.