B2/W2 have always seemed fairly balanced to me, but I've always felt that Black and White are the hardest games in the series, if only because Gym battles are so hard that it feels like the game expects you to stop and make a completely new team to deal with whatever Gym Leader you're dealing with at the time. Since we were stuck with just the new Pokemon for those particular games I suspect they may have done this on purpose in an attempt to encourage people to experiment and use the new Pokemon rather than sticking with the same team through the entire game. OR maybe I just took constantly losing to the evolved form of the obligatory first route rodent and the obligatory Pikachu clone in certain Gym battles too hard and decided to always go to extremes to make sure it never happens again. Or maybe I'm just terrible at Pokemon, I dunno.
As for Audino grinding, while it did make grinding a bit easier, you still had to actually find Audino for that to be of any help. At least in the first games, I don't know how many times I would run up to some shaking grass expecting to find an Audino but instead got an overpowered Zebstrika that would one shot whatever Pokemon I was trying to raise at the time.