if you strictly prevent the manipulations that character would naturally employ, you break the pattern of the language matrix you're relying on for their intelligence.
While I do not strictly agree, this points to a deep insight.
there's no guarantee's on who ends up on top and what the current cleverest character is like
In my experience, HPMOR characters make clever simulacra because the "pattern of their language matrix" favors chain-of-thought algorithms with forward-flowing evidence, on top of thematic inclinations toward all that is transhumanist and Machiavellian.
But possible people are not restricted to hypothetical humans. How clever of a character is an artificial superintelligence? Of course, it depends on one's ability to program a possible reality in words. The build-your-own-smart-character skill ceiling is unfathomed even with the primitive language matrices of today. The bottleneck (one at least) is storytelling. I expect that this technology will find its true superuser in the hands of some more literate entity than mankind, to steal a phrase from an accomplice of mine.
thus far the best solution I can think of are some very, very well-written police.
I don't think police are the right shape of solution here - they usually aren't, but especially since I find it unlikely that an epidemic of simulated assholes adequately describes the most serious problem we'll face in the 21st century.
You may be onto something with "well-written", though.