If the tier were poorly designed, then there would be no discussion on it. A sim would simply tell you the answer and that's that. Re-using mechanics we already had in place before MoP or making something that is not obviously easy to math out (note that this does not imply it is impossible, either) does not constitute a poor design. A poor design is determined by how well or how poorly the design satisfies the design criteria.
The fact that this discussion exists (for both tanking and DPS (except DW Frost)) and the fact that there is not a clear answer is exactly what the developers were aiming for with the MoP talent system. Whether you personally like the tier is another issue entirely, but the fact of the matter is that this is one of the most closely balanced tier choices that actually impacts your DPS and rotation in a meaningful way. In that regard, they have done exceptionally well because it is exactly what they set out to do. Sure, they didn't get every tier right, but this is the one tier where they absolutely did.
However, this is a tangent.