Yeah but if all 6* deserve a A Tier or S Tier it would be too balanced and tiering would be meanless. A good and balanced power repartition should be very rare S Tier, few A Tier, a great amount of B Tier, a small amount of C Tier and a few D Tier. If we dont get this, maybe we should rethink our tiering system.
Right now we have a lot of A Tier but that because we just started and most of the very old 6* are amazingly unbalanced at all. As you said, the newer ones would be more often B Tier or C Tier with some exceptions.