Rocksteady had from August, 2009 to October, 2011. Nearly two years to work on a sequel that brought a completely new environment and features and isn't a glitched mess. WB Montreal had from October 2011 to October 2013. Do the math, now. Two years to implement new stuff but reutilizing nearly everything RS had built. They didn't build this from the ground up, they already had a lot of stuff done to work with. But, unlike the others, this one has mp...and freezes, glitches, bugs.
How much of the budget went to Splash Damage for the development of mp? How much of that could have gone to the sp? To refine it?
Development time most likely wasn't the problem here, because not only they already had a ton of stuff done by RS, but I'm also still facing glitches after the patches were released.