Perhaps when the army was small pre-1914 it was possible to see it in a more individualistic way, whereas with the mass armies post-1914 it was harder to do so.
I don't think that is the reason, or only reason. I think its the change in warefare that made the difference for WWI. In a more or less static trench warefare its hard to find public heroes. I don't have numbers, but I would guess that most of the soldiers that got VC's in WWI were normal heroic soldiers, with the tiny problem that their acts of heroism did not fit the need that the country had to inspire them.
So generally, I have this idea: fighters pilots are heroic because the values and ideologies of society at the time were conveniently able to mold themselves to accommodate the military aviator. Pre-existing values and ideas, such as that of the public school ethos, sport, chivalry, jingoism, militarism etc as shown in popular, patriotic and juvenile literature, were placed onto what the aviator did. Because of this a generic heroic view of the airman arouse quickly, helped by the press, politicians and some aviators themselves. However if we take the hero to be someone who performs an act of bravery, valour, courage, devotion to duty etc, the fighter pilot cannot be a hero in this general sense. The fighter pilot fights in the air as the foot-soldier at the front does: consistently. HOWEVER...it is the nature of the combat itself that separate this similarity and places it as exemplary. The aesthetics, along with cultural, literary and social perceptions of aerial warfare made it heroic and by proxy made pilots heroic. 1v1 combat, duels etc were exciting literary conventions into which the pilot was placed. There were, of course, single acts that, if we took my idea that heroism requires a single act, were heroic - like Robinson shooting down the SL11 or Bishop's attack on the german aerodrome, or Voss' ill-fated yet determined fight against 9 or so enemy pilots.
I am not so sure about the public school ethos, remember most countries made their aviators into heros which means that unless the public school ethos excisted in all these countries it would not necesserly be a part of the package. Other than that I think you are on the right track. Comparing WWI and WW2 could be worthwhile too if you can fit it into your thesis (and I would very much like to read it ), there must be a reason for Britain to break with the practise from WWI while Germany continued with the old practise (and expanded it).
So I guess that, if I am correct, that heroism does not necessary need a heroic act as such, but for the pre-existing structures and cultural/literary backgrounds to exist that can mold a heroic image onto a person, or people given a particular situation, in this case war
If the goverment/media think we need heroes we will get them, even in the cases where no heroics have been displayed. Think Jessics Lynch.