Then there's the observation that a lot of voters certainly seem to want the President to be a dictator. Eras are routinely defined by presidential decisions, and Presidents are blamed for just about any political failure (though not necessarily always credited for successes).
The unitary executive theory is a theory about the structure of power within the executive branch (not the scope of executive branch power) under the US Constitution, so its not even a theory which applies to any other country, nor is it relevant to the relative balance of power between the executie and other branches (except insofar as strong versions of it restrict the legislatives branches ability to create final authority other than President elsewhere in the executive branch, but that's rarely relevant, one way or the other, to the President's ability to keep substantive campaign promises.)
> Then there's the observation that a lot of voters certainly seem to want the President to be a dictator
The things you point to to support this seem more like people acting like the President actually has the power of a dictator than actually wanting the President to be a dictator. (And, in the case of defining eras, seems more like "Presidents are convenient simple symbols" than anything having to do with dictatorships; this is more related to the ceremonial chief of state role than the substantive head of government role, the US system just happens to unite them in one person rather than having a separate King/President for the first and Prime Minister/Chancellor for the second.)
Actually, most of it is an indicator of just how strong the other, coequal branches of the overt, Constitutional government are (particularly Congress, but the Supreme Court has a role, too.) The President is not (even before considering the influence of any "shadow government") a dictator, and most significant policy changes require Congressional action, or at least acquiescence.