Well prequel Yoda engaged in battle with Palapatine for about 15 minutes, then fell down and gave up and decided to hide on Dagobah for 20 odd years, he's already kinda an expletive.
I don't have an issue with the tree zapping, my idea of force ghost are more like projections of the viewers subconscious mixed with the Force, and the Force is itself a thing so whether Yoda summoned a bolt of lightning, it was Luke's subconscious, or the Force itself reacting to the interaction I think it makes as much sense as any Force Ghost concept.
I also do not think the Force and Force Ghost are separate entities, as when Yoda died in Jedi he said he would be one with the Force, so where does Ghost Yoda being and the Force end? That's why no matter how powerful a Force Ghost appears I don't think they can go round serving old allegiances, and besides their likely to only have such power where the Force is particularly strong.
I mean if you think Yoda could have Chuck Norrised the whole First Order, Obi-Wan could have at least done espionage work for the Rebellion, all those Bothans would not have had to die if a Force Ghost has memorised the Death Star plans.
PS: If Force Ghosts don't interact with their environment why does Obi-Wan sit down on the log in Jedi, do ghosts get tired?