People often don't do the most rational thing when falling to their doom
One would naturally assume that falling might be a good focus breaker, and that the lightning would have ceased. But he continues firing aaaaaaaaaallllllllllllllllllllllll the way down.
Vader grabbed him in his tickle spots?
-1 for the laugh.
More likely that Palpatine was surprised and doing the Sith Lightning equivalent of flailing around trying to fry Vader before he got tossed. And after he got tossed he was just angry about it and lashing out.
But Sidious is a survivor. I doubt he would waste time pitching a fit. That's Vader's shtick. Maybe it's just that good ol' Sith tenacity. I'm not going to stop my attack from a mere hiccup.
I like your thinking on the first part. However, Sidious trusted no one. Especially Vader. The Emperor ruled through fear. So the less you had to fear from him, the greater the liability you were. Vader would have had the greatest chances at direct resistance, ergo
he was the greatest threat to Sidious' reign. Haven't read, but I've heard that Lords of the Sith highlights their relationship, and how Sidious gave him sub-par prosthetics so that he would be more easily managed.
Did the Sith Knights under Revan's Sith Empire have the title of Darth, or did they simply use their real names?
I don't believe the title of Darth was ever freely handed out (until Saber Forum
). It designated a certain level of skill as well as dedication. Similar to the Sith Acolytes not being at the same level as a Sith Lord.
In the Bane trilogy, Darth Bane reasoned that the Brotherhood of Darkness was actually afraid of the title, and what kind of power it represented. When Bane embraced his destiny as the Sith'ari, he reinstated the title's use, as he would make sure it was bestowed only upon the worthy.