I agree with you. I used to count the number of Bush vs Gore/Clinton jokes Leno used in his opening monologues. It came out about even most nights. There was a time that I wasn't totally convinced that Leno was a Lib. because of it (naive, I know).
I stopped watching him many years ago so I don't know how much he changed since.
It’s my understanding that when the choice for the successor to Johnny Carson was still unresolved, that Letterman seemed to think he had a birthright to take over the show due to his many years of holding down the late late night position, but the numbers that Leno produced both as a comic and as Carson’s permanent guest host suggested to NBC that Leno had a wider appeal.
To his credit, Carson reportedly refused to take sides and would not endorse one potential successor over the other although he apparently emphathized with Letterman over what appeared to be a deliberate shafting by NBC.
In the end, NBC was right to do so and lost nothing by Letterman flying the coop.