It's true that if a mission that requires small group of people, a fireteam or a squad would be sent on some kind of spec ops mission. But most of the time in WW2 it's actually a platoon or a company that would be asked to hold a position until a certain time for the relatively larger army to escape the enemy's cauldron. These units would be a permanent type, not temporary ad hoc units put together in the last minute. No matter how romantic it is for holywood movies, a squad is not enough in most cases, as it cannot function independently, only a division or larger unit could do that. In Star Wars what they could have done is have the Inferno Squad to be a strengthened unit of, let's say 20 fighters. But for some reason in the book before their "current" mission, all the other ones were lost in combat/missing in action so that four of them were the only ones left.