It's weird, though... so many people complain about the hit detection (even with ADP through the roof) that I wouldn't doubt there being something odd happening. I don't have a lot of hit detection issues in DkS2 personally, but maybe I don't remember too well, or maybe my whiffed attacks should have connected and I just shrugged it off.
I've shared my opinion on the DLC here, but I understand Kieran's frustration. One thing I noticed is that, for good or bad, sometimes it's hard to pinpoint exactly just what the hell DkS2 is trying to do.
If it helps, I did the whole DLC in NG++, and I played through it in the mindset of knowing I'd be frustrated somewhere, but also that I would see interesting things. Overall, that was the ideal mindset for me. Sunken City was a blast to explore, I took my time and really enjoyed the nuance of the level design. The bosses, not so much. The other two DLCs were more of a struggle, but I'm convinced now it's probably because I was anxious about being in NG++ and not wanting bosses to take forever to die (which they do, and I still don't agree with). The level design in Iron King and Ivory is definitely interesting enough, often brilliant.
I'd say they're worth slugging through, despite most of the bosses being really uninspired. I don't agree that they're among the best in the series, not even Sir Alonne, which is a pretty cool fight. I feel that Artorias of the Abyss handled the bosses much better, making them increasingly more epic (sorry for using that cliche word), challenging, and not relying on recycled content, numerical advantage or super long treks to make them difficult. I generally don't mind running a long distance to fight a boss in these games because there's always a way to make the trip less painful and I kinda enjoy figuring it out. But I guess because I was in NG++, the added Black Phantoms, overall enemy defense and boss HP were a little discouraging every time I died. It's like they want you to consider despawning enemies as a solution, but they don't necessarily understand how much of a bore that is if you're doing it on purpose. It's a trade, but not the best trade in these DLCs because (again IMO) for the most part, the bosses aren't worth the long trip.
Nothing I'm saying here is set in stone, though, it's just impressions and I could be wrong. I will definitely do the DLC in regular NG one of these days, and hopefully will change my opinion for the better.