The issue with the ground noise is
wrong..
...that's come from
wire mesh C Band dishes where it is true ....but
it works the other way for solid metal dishes ....(er... not that solid in the case of the Fortecs

).
Wire mesh reflects C band OK but lets x amount of noise through.... the solid metal KU band dish
shields the lnb from ground noise and it just points up to the satellite...
The offset's lnb is then potentially more exposed to ground noise directly- it sticks out and aims across the Earth.
There are other issues that aren't right in you lists... I'm not biased either way, I've put people off the fs 2.4s before now and avoided doing them... but there's more swings and roundabouts that only a decent side by side test would give the acid test result....
I like the focus theory though. not sure it's right but I still like it.....