In terms of giving a morale boost, one could refer to an inspirational or totemic leader. As a noun, a leader could simply be described as an inspiration, although this is a broad term that can refer to any inspiration. If someone gains power/morale from being supported by their troop, they can be said to have been rallied by the troop, and in return they can rally their troop. As you suggested, the leader could also be motivated by their troops, or motivate their troops.
In a civilian as opposed to a military context, there are all sorts of positive adjectives one might wish to assign a good leader who boosts their people's morale. Some of these could be competent, charismatic, and charming. A great leader may become famous and/or celebrated.
I don't know of a phrase where someone can so generically point out a flaw. In your example, I'd say human - nobody is perfect. Perhaps his weakness or limitation would fit here.
There are words for dramatic flaws.
An Achilles heel: a portion, spot, area, or the like, that is especially or solely vulnerable. It does not need to lead to his downfall; it connotes someone who is pretty damned perfect except for this one thing. "Tom Cruise has an Achilles heel" would be understood that way.
His Achilles heel is his quick temper.
Shortcoming, or foible would be understood as an understatement; if he's crazy, that's a major problem; to call it a foible before stating the flaw would be mildly sarcastic.
A tragic flaw in drama is a failing of character in the hero (someone of high repute/honor/etc.) of a tragedy that brings about his downfall. Regarding Hamlet:
He has exceptional qualities like graceful personality and popularity among his country that is eminent. His tragic flaw is his delay in action and irresolution...
Other expressions for this are simply flawed, or inadequacy.
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Such a person (as Darth Vader, not an ELU moderator! :) would be called a...
The adjectival form megalomaniacal does occur, but it's nowhere near as common as the noun.