No. Voyager always emphasized the hierarchical nature of the military. The easy assumption that the starship captain will have the kind of authority modern military commanders (or Hollywood producers) have is essentially rather conservative, but modern Trek has always been much more conservative than Star Trek. But given that standard, Janeway was not tyrannical at all. Every single lead character if I remember correctly defied her at one point or another. She is actually rather forgiving, but maybe circumstances forced this?
At any rate, I know of no reason whatsoever to think Janeway was tyrannical and was for a long time puzzled by these attacks on the character. Insofar as these people try to offer evidence, it usually rests upon the interpretation of the Prime Directive. Unfortunately no one actually knows what this requires (whether they imagine they do or not,) so it is impossible to lay any weight upon alleged arbitrariness in the character's personal interpretation.
The few other instances offered in support usually display extreme misunderstanding of what actually happened on screeen. For instance relieving Chakotay in the Equinox two-parter was not tyrannical, not even extreme, because Chakotay had just helped stop a hot pursuit of a Federation vessel actively engaged in criminal activity. The script wrote a miracle to get him off the hook so they could find the Equinox again but that was the arbitrary action in this episode.
And so forth.
And I suppose that to you, Janeway broke no rules when she was willing to let Lessing die?
You are making an assumption here (that she would have let him die) which is not necessarily true. Because Chakotay intervened, we don't know that she would have allowed the little beastie to kill Lessing.
But, I have another issue with that--Lessing is a traitor who was willing to sacrifice Voyager and its entire crew to save his own skin. I'm not condoning torture, but I can understand why Janeway might have been a bit testy about being betrayed.
But, no matter what, we don't know if Janeway would have allowed him to die.