I have a Major George Preddy from UltraCast. He's sitting on the cockpit wall like he's entering/exiting. I got him to liven up a Hasagawa P-47. (Yes I know he flew a P51 but I prefer the 47 so that's where he's going)
I also have a great looking pair from NEMROD, Naval aviator with crewman in resin as well for an old Revell "Smithsonian Series" F4F.
I also have some 1/48. A nice resin Richard Bong by LEGEND and a couple from EDUARD: Luftwaffe 1944 with 3 pilots (2 seated, 1 standing) and 3 ground crew and the US Navy Personnel 1942.
I've seen a few offerings of WWI pilots in 1/32 as well but you are right, if you want 1/35 infantry, tank crew and the like, especially Germans, you have an ocean to pick from. I guess this has to do with the display/diorama potential.
There's not a whole lot you can do with an aeroplane beyond the standard "servicing scene" or perhaps "crash scene" but having a standing figure really helps showcase a standard display in my eyes.