Other mistake: In Finn's attempted sacrifice, there are plenty of logical inconsistencies. First, Rose's pod is to the side or behind Finn, but manages to beat Finn's pod to the cannon. The collision had a similarly high chance of killing Finn as would ramming the cannon. Finn then carries Rose back to the hideout faster than it took the speeder pods to reach the cannon.
Plot hole: By having Admiral Holdo perform her infamous hyperspace ramming stunt, Rian Johnson created a continuity problem with the rest of the Star Wars universe. Since this maneuver was successful, every space battle before and since should only include a droid piloting spacecraft ramming enemy bases through hyperspace. This tactic would have been more cost effective and less risky than full on space battles seen in previous films. This tactic would no doubt have been tried in a universe filled with space battles often with disposable troops on both sides, such as in the Clone Wars. The Death Star did not need a successful trench run to be destroyed, just an X-wing with a droid ramming it at hyperspeed.