If, as has been suggested, Poe believed that the attempted attack on the gun was going to fail and he called off the attack for that reason, that looks less like a character arc for Poe than a practical decision, just as he made in successfully attacking the Dreadnought.
If Poe had not destroyed the dreadnought, would its guns have been successfully used to destroy the rebel ships during the later pursuit, or alternatively the Crait base?
Save who you love don’t fight what you hate.