I'm not going to extrapolate on this very much because if you can't see the flaws in the gameplay of "capture the point" style games in non-FPS games, you obviously don't care about game balance...
- Ranged champions will be disproportionately powerful
- Localized AE effects (Anivia, Cass, Gragas, Lux, etc.) will be overpower because positioning is forced by the game type.
- Capturing points is a less effective strategy than simply pinning a team in their spawn
That should be enough obvious downsides for now.