Yeah but the First Order launched a fighter attack that took out most of the Resistance leadership, and after that success they decided to not do that anymore. They could've easily spotted any ships trying to escape if they had their fighters constantly harassing the Resistance ships.

So the idiot Resistance plan was to count on the First Order to be idiots. But while they were idiotic enough to not continue using their fighters (which were super effective), but not so idiotic as to not look out the window.

Have some sympathy for Holdo! When you're an idiot in an idiot plot, it's really hard to judge how idiotic your enemy will be.