I'm not sure what you think an attraction consists of, but both the Liberty Belle and TSI are attractions, which will be replaced by two Cars attractions, resulting in 0 net attraction gain for MK. Even if you just focus on rides specifically and not attractions in general, it's only a net increase of one (add 2 Cars rides, subtract the Liberty Belle ride). Now, if they kept ROA and TSI intact, and added the Cars attractions on an expansion pad, it would be a net gain of 2. Attractions are a big part of the WDW experience, but so is theming, atmosphere and setting, which is what TSI and ROA provide to that whole quarter of the park. If we start removing that for more rides, then MK will become more of an amusement park and less of a theme park.