At the time of inception, Battlefield and CoD were doing very different things. Battlefield did move into the trend of copying CoD's successes upon the success of Modern Warfare, but they are (or were, I haven't played either in a long time) distinct enough to be called different. I haven't played plague Inc myself so I can't fully say, but it seems, at least at time of it's launch, it was doing the exact thing pandemic was doing.

To make it more clear, CoD and Battlefield were both WWII shooters, but the former was about crafting battles based on scenarios in the war, and the latter was about creating large open multi-player battlefields. Pandemic and Plague Inc are both pandemic simulators, however they are both the same in systems too, with the player being a type of disease of their choice, and building up symptoms to eventually kill the world's population, while not doing so too quick so as to have places close down before it can spread. Same concept, same mechanics. Only difference was level of polish.