I echo Winston's post - if you need really strong A/C aftermarket might be the better way to go especially since factory AC is already hard to find.
I had many 80s and 90s MB with factory A/C and it was at best helpful in evaporating most sweat in those hot muggy summer days in New England. My 2001 CLK55 AMG was my first Benz that had proper cold AC
If it were me, I'd daily drive something else - a Toyota 4 runner to stay with the overlander theme - in summer. When the weather is barely warm (those rare 70-80F days in San Francisco), I really enjoy driving the G without AC. With the windows down it's very airy unlike modern cars especially the big sunroof open. Not sure if it's a shape of the car or the fact that the windows are big?
2018 G550 | IG: @gunthergwagen