What equivalent rate is trying to hold constant
Equivalent-rate conversion is not about making two nominal rates numerically identical. It is about making the annual growth outcome identical after compounding is taken into account. If two rates produce the same effective annual yield, they are equivalent in compounding terms even if the nominal percentages differ.
That is why a monthly-compounded nominal rate is often slightly lower or higher than a quarterly- or annual-compounded quote when both are translated to the same annual growth result.