The stripped-down Lightning Mode of the Storm Megazord doesn't last very long. You might wonder why they bothered, but this is a Merchandise-Driven show. The mode with parts removed doesn't last very long, instead reverting back to the full mode, because this encourages young viewers and toy owners to not take the parts off the Megazord toy for very long and thus risk losing them.
Except that's not how the toys work. The toy can't turn into Lightning Mode, Lightning Mode is a seperate non-transforming toy of it's own.
Lothor says they can't attack the Rangers in their civilian form because a Ranger's powers can only be destroyed when they're in Ranger form. This makes sense, as if they just killed them, their powers could be given to someone else. Destroying the powers themselves is a much more effective way to permanently claim victory.
Except that it circles back to fridge logic, because we've seen Ranger Power destroyed before... such as when the Power Coins were destroyed by Rita and Zed, or when the Turbo Powers vanished when Zordon's world was conquered. In the first case, they weren't in their morphed forms then... So Lothor isn't making any sense.
Sure it does, in both those cases the villains eliminated the source of the powers rather than the powers themselves. Though we don't know what exactly happened with respects to the Turbo powers, the red and blue rangers were able to morph again using new morphers so maybe they just lost the connection to the source in that case.
Sensei's body-swapping in Sensei Switcharoo offers a two-fold: first he's switched with Shane. When Sensei was a student, as shown in the Samurai's Journey trilogy, he was a student of the Air discipline; very fitting. However, when he ends up in Dustin's body, it adds a touch of irony, given that it was his brother Kiya (Lothor) who was an Earth discipline student.
Why did Lothor go from a serious villain to a more comic relief villain makes since if you remember his Fourth Wall Awareness. In other words, he knows what happened to Lord Zedd. After Zedd's first appearance, parents complained and thus he was toned down to make him less scary. Not helping that he also knew that he was on a Disney kids show, thus there was a chance that he would suffer the same fate, if not worse. So he decided to invoke his own Villain Decay before Disney could do it themselves.