BC2 was a fine game by itself. I mean, it did have some wonky design choices, oversights, and balance problems, but what BF doesn't. My hangup with BC2 is basically two-fold:
First, it's just about as antithetical to Battlefield as you can get without becoming COD or <insert serious business small-scale esports shooter here>. What makes BF special, what makes it stand out and what made it such a joy despite being mechanically behind the curve for so many years, is the premise of the combat sandbox. Big, open-ended maps, lots of players, lots of tools, and lots of ways to play, which also meant the ability to dictate your own tempo/pacing. BC2 took that formula and cut it way down, becoming a smaller-scale game about funneling people down down linear map chunks where everyone collided on tiny objectives. It became less about freedom and creativity and more about the meatgrinder. It's the kind of 'streamlining' that I don't like.
The other angle of this is that, release-wise, BC overlaps with BF, or is at least likely to. I want BC2 fans to have BC3. What I don't want is for BC3 to come out at the expense of a mainline BF title. If DICE could manage to work on both simultaneously, that would be the dream. Everyone wins. Though given how much of a little strugglebear DICE has become, I'm not convinced they can nail either BF *or* BC right now, let alone manage to juggle both. :(
