Some quotes from the real argument, with the parts that were in particular ignored highlighted.
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.
As everyone knows, Chakotay's interference prevented us from knowing what Janeway would have done a few seconds later. But this simple fact is commonly ignored. But let us hypothesize that Janeway, whether intentionally or by misjudgment, had actually let Lessing die.
I reject your argument from depravity that equates Lessing's imaginary death with an injustice. Lessing murdered people, of an unusual and technologically primitive sort, it is true. But he was still a murderer. It takes barefaced gall to whine about Janeway breaking rules in the purely hypothetical case of Lessing's death, while blandly pretending that she didn't also break rules in allowing Lessing his freedom.
Lessing got away with murder because Janeway was a tyrant? She was too soft on him. Letting him off just because he was following Ransom's orders was highly objectionable. He was even worse than the Maquis.
As for the assumption that Lessing was tortured, Janeway didn't personally threaten or harm him. She merely left him outside Voyager's protection so that he would face the fellows of his victims. The notion that humans are so privileged that ugly primitives have no right to exercise justice on them, even upon murderers, is absurd. And it may be a science fiction story, but that way of thinking still smacks of something really ugly.
It is neither law nor justice nor simple common decency to require that Lessing face only human justice for his murders. It is also a dishonorable way of assuming the conclusion, that Janeway did something tyrannical. That kind of fallacious argument is absurd but we still have to take it seriously in a way. To say something so foolish shows that there is some prejudice clouding the mind.