I tried your suggestion with the mesh patch but KLAS still seems to be sitting on a hill,the plateau is not as steep/sharp as before but there is a definate rise on approach to the airport.
You will never be able to fix it entirely.
The real world airport has a significant slope gradient, but Flight sim doesn't really support sloped runways (the tricks some developers used to simulate them wouldn't work on such big airport, and would kill AI traffic) so, you will always see some rise, especially from one side, to give the illusion of a fix, it would required to smooth elevation for a very large area around the airport, which kind defeats the purpose of using better mesh terrain to begin with.