Thanks. That makes sense.

I now have a lot more to go on than what I had previously. I have been to L.A. once for work, Santa Monica specifically, and that was my first thought. Go to LAX and find somewhere nearby. I didn't really consider LV because it's a dessert, so what is there to see? But I can see from some of the places driving distance away, that it might be worth going there then getting a car.
Similarly, I know nothing about San Francisco other than it has a big bridge. Looking on Komoot, there appears to be some highly ranked rides all starting from close to city centre. And then San Diego has been mentioned, again, I know nothing about this place with the exception of what I have seen in Anchorman. A quick look on Komoot and I can see some rides close by which are akin to what I was expecting from going to LA area.

Based on everything I have read so far, it would be:
San Francisco/San Diego - Rent a bike in the city and cycle out from there
Las Vegas - take my own bike and hire a car to get somewhere good, then also do a few midweek cycles round the local area purely for time in the saddle

I cannot see me changing flight in the US as I have to change in the UK anyway (I live next to a provincial airport as it is), unless I see a direct flight to the US appear (currently I can only get to Orlando or Toronto direct and its costly). There may be an option I could fly to Atlanta, Boston, Chicago, New York, Orlando, Philadelphia or Washington D.C. direct, and then change internally to somewhere provincial. However, I want to keep the travel to a minimum. I would want to spend 3 to 4 hours in an airport and/or the same again in a hire car (unless there is something truly special).