Biomarker evaluation - c-statistic (AUC) and alternatives

My understanding is that the C statistic of a simple model is interpretable and is an essential metric. What I intend to convey is that comparing C statistics is difficult to interpret. Adding a new factor to a model typically yields small improvements. For example, from 0.70 to 0.72, the practical interpretation of such a result is unclear. Or is this difference interpretable?