Was difficulty nerfed in general?

I can think of a couple of things... The first is that if it has likely been your first playthrough without the long service bonus to XP gain in a long time, so you're probably at a lower level than you were at the same points in the game as you are now.  The second is that, potentially, in buying DLC weapons and armor, you're not buying the same health-related upgrades that you did in the past, so you're running with less health than you're used to at this point in the game.  You may have also been used to wearing DLC armor that also provide boosts to health and shields that you're not wearing now either because you haven't found them yet to purchase or you haven't yet got the lab and materials to research them.  Those DLC items used to be available in your inventory as soon as you got the Normandy.

I really don't think the difficulty of ME2 has changed at all.  Once I got my usual weapons and armor, it never felt harder than previous runs.  When it's felt easier than before to me, it has been due to numbers of enemies failing to spawn.  I would replay those inordinately easy battles again and, if all the enemies spawn in, it felt about the same difficulty as it always has before.