Holdo staying behind to be the ‘captain going down with the ship’ wasn’t well earned, as it was only really her ship for a couple of hours.
Someone on this site might correct me, but isn’t the Cruiser the same one that Ackbar commands in Return Of The Jedi? Having Ackbar stay behind to do the hyperspace ram would have been an epic end to a fan fave, far better than the derisory off screen death he recieved.
As for Ackbar not telling Poe the plan, that would be an easy fix - “loose lips sink battleships” and for a character who famously found himself in a trap before he’d be keeping tight lipped for sure!
I think the sacrificial lamb should have been Threepio. Firstly, it’s absurd that they didn’t use a droid for the final run. Secondly, I think Threepio has been woefully neglected as a character over the years. It would’ve been amazing to have Threepio go out in a blaze of glory. Imagine him saying something like “bravery is not part of my programming, but I will do what I must!” (or something)…