It's because even with a patrol you are capped at -15 below the enemy. All the new content, except for possibly the raid, caps you below the content. There's no point in increasing your power, as you won't even reach parity. Bungie claimed this would be a more inclusive expansion as they wanted more people to experience the content. Instead they lied, upped the difficulty across the board, and effectively have made Increasing your power pointless.

This is the main problem, imo. There are tons of ways they can make things more difficult if they absolutely wanted to. But, the one thing that ruins it all is the light level capping. The only reason the normal campaign mode became tolerable for my 2nd and 3rd characters, was because I was able to overlevel to the point where the Calus fight wasn't excessively irritating to me. Capping the lowest level of Nightfall, and the entire planet of Neomuna, among other things, is what makes this DLC so frustrating because we will never be able to over level this crap to make our experience fun. And, yeah, some people like it and the difficulty and that's fine. But, I must sound like a broken record by now simply asking why we can't have our Adept Nightfall back, or at least the ability to turn off the level cap.