He did apparently play Eisenhower in "The Butler," but I had been wondering if the failure of "The Crazy Ones" and having "Night in the Museum" be his current claim to fame had had any impact on his self-perception.
However, what you're saying about control and power doesn't really seem to jibe with the Williams that people seem to be describing. He seemed more down to earth and genuinely kind than finding value in his dominance. I can't speak about whether he felt his creativity was on a decline, although his branching into drama from comedy would have been one way to inure himself against that. It's not like he wasn't successful in multiple venues, and comedy was just the "high octane" one. He had more to live for than just that, so it sounds like there are other factors involved.