It's bad to get too caught up in these "level" discussions - some have meaningful features different, some do not. Apex, as near as I've ever seen, is Rival with a bit more plastic instead of carbon. Sort of how Super Record is a slightly lighter Record with a bit more Ti. Tiagra, for better or worse, is the old 105, with the old side shift cable routing and large, bulbous hoods, while new 105 is mechanically different and more similar to current Ultegra and the previous DA. Similarly, Force and Red have mechanical feature differences to Rival. If Rival competes with 105, Apex does as well, and Tiagra is a different class.

Sorry if that isn't clear; I'm a bit sleep deprived.