No one is perfect, and therefore it’s not necessarily reasonable to expect a character to make all around perfect decisions (as FilmCritHulk points out, there’d be no conflict if so). There’s obviously supposed to be an air of suspicion around Holdo at first, which is why we question her decisions and don’t see her perspective and decision-making (only Poe’s). In the end, we learn her heart and mind were in the right place, and her plan would’ve worked just fine if not for Poe.

As for why she didn’t lock up Poe, I don’t think it’s illogical at all to think “I don’t want this guy in on decisions or on the bridge, but I don’t think going as far as literally jailing him is necessary, especially when his biggest crime was disobeying one order and yelling at me.” Not sure why it’s a binary “either tell him the plan or lock him up,” that’s doesn’t sound like the only acceptable logic to me at all. Holdo didn’t trust Poe with the plan. That doesn’t seem crazy to me. Her biggest mistake was actually underestimating how little she should trust him. Again, not perfect, but there’d be no conflict if she was.

As for the logic of her plan, I don’t think we need to have that endless debate either. I don’t know if if it’s Cinemasins or just years of nerd porn EU books misleading a certain generation of fans to think this is a hard sci-fi franchise, but for some reason people love to nitpick the “logic” of these things to death as if the main determiner of a film’s quality is the “realism” of its wiki plot summary. I’ll just say what I always say: cinema (and fantasy and Star Wars in particular) is about the possible. It’s just as easy to come up with a reason to explain away these perceived “plot holes” as it is to claim they’re “impossible” to explain and therefore movie-breaking. I don’t think it’s worth it to worry or waste time with the latter.