About the Dreadnought destruction:
In the moment it isn’t heroic. There’s a shot of Poe looking at Paige’s bomber falling into a fiery inferno and he does a sad face.
And then while everyone’s celebrating on the cruiser, Leia looks at the death toll and sighs.
The movie’s take on self sacrifice is: Useless self-sacrifice is bad. Paige didn’t need to die. If the battle had gone differently, she would have lived.
Holdo needed to destroy the Supremacy and only had one way to do it.
Finn’s self sacrifice wasn’t needed because it wouldn’t have changed anything.