That's maybe half correct at best. Jay Leno could only take a small portion of his audience with him from the Tonight Show, if he chose to set up a competitor show. The same is currently true about Fallon, and likely far worse in his case today. Conan could never match his audience potential as host of the Tonight Show (pretty much no matter what he does, and certainly not on cable at TBS), because of the value of that specific platform, built up over decades and given its prominence on NBC.
A very large share of the Tonight Show audience, stays with the Tonight Show, regardless of host (barring the next Johnny Carson abandoning the show, or a truly horrendous product implosion at the current show). That audience largely belongs to Comcast NBC.
If Jimmy Kimmel leaves ABC, he would be replaced. Kimmel would struggle given the limited options, ABC would simply plop the next Kimmel into his spot and move on, with a large percentage of the same audience giving the next person a try.
Craig Ferguson's audience did not go with him, as another example.
The effect of this being that all late-night talk show hosts are always subject to a direct financial comparison (but fortunately for their audience is sticky and belongs to them personally not to the television network). With top AI researchers, there's no real comparison or stack ranking, it's all about passing a certain bar which is objectively evident based on their past work, at least as long as AI is hot.