I don’t find that this adage applies that well in politics. Yeah, I’ll assume whoever almost hit me with his car the other day was stupid/irresponsible/distracted rather than that they were attempting to murder me. Or that someone who gave me wrong directions to somewhere was mistaken rather than deceitful. That is because stupidity can explain these things, but stupidity on its own doesn’t explain becoming president.
Beside, if you assume he was being used by dickcheneys, you’re still assuming malice, just not from the same person.
As for which case his behavior would make most sense in, I won’t try to contradict you since I’m not good at analysing people and don’t enjoy trying.
I just tend to think of Trump+close collaborators as a system and assume the purpose of a system is what it does, and I don’t make too many assumptions of Trump’s exact place in this.