the best setting if only because the mechs are so jank that for a big chunk of the game's timeline cockpits overheat to the point that half-naked is the actual official pilot gear
Basically at the very least, you need the pilot helmet since it's the thing that makes you connected to the 'Mech with the neural interface shit, but depending on the year and/or faction, you'll have to go in on your underwear, or you get a cooling jacket/vest, or if you're really up there you get a proper pilot suit
It's just a lore thing. Also MW5:Clans being set in the Clan Invasion of 3050 should mean everyone's tech has gotten back to "wearing a proper pilot suit" level