I have no problem with Trump making the decision. My point is that Tillerson's policy differences with the President are more of a reflection of the State Department's views and the effect they have on Tillerson than anything else. Pompeo will have to deal with the same kinds of problems. Will he buck the institution's views thus engendering a backlash among the bureaucrats who will then seek to undermine him or will he go along to get along recognizing that his perceived success depends on the support of the bureaucrats?
The bureaucracy has many ways to knife the political appointees in the back without being held accountable. Leaking is a very powerful weapon.
Tillerson was attempting to undermined Trumps agenda regarding Iran.
Tillerson had to go. End of story.
It's for darn sure that Trump does not appoint an agency head to be the tail wagged by the dog, the agency being the dog. He definitely believes in hierarchal organization, and wants his agency heads to be in charge. And he definitely wants to be in charge of his agency heads. His antidote to this is that he is long reputed to be a good listener who takes advice. But he is clear that the role of the executor is to spearhead policy, make the critcal decisions after receiving research and advice, and see that they are carried out.