I think we agree on that.
Narcissist, certainly; immoral and corrupted, most likely; but still possibly rational [0], I see no reason they'd be de facto irrational despite how I feel about them. Born autocrats (or born in a line of succession) are a different story, but I'd argue it would even be unlikely for a commoner to ascend to absolute power without starting off as a rational, calculated and intelligent person (tho ofc not impossible, there are obvious cases). Not that there is any guarantee they'll necessarily remain so, seems unlikely after years or decades being surrounded by sycophants.
Feel free to disagree.
0: https://www.oxfordlearnersdictionaries.com/definition/americ...
Survival breeds sycophants, ...
Shit, why am I reciting stuff from 8th century BC here?
Sanity (Oxfod, 2nd def) :
>the state of being sensible and reasonable
Morality is indeed besides the point, I just added it as I feel dirty suggesting he's rationale 3 days after invading Ukraine without amending the idea.
As for mistake, I think speaking of a political mistake is relevant if we should consider your explanation wrong, i.e. he's sane/rational autocrat whose invasion backfired more than expected, should that be the case.