Thunderpocket, your failing is that you assume it's hard to see a plane and keep it in visual sight. In fact it's probably a million times easier in real life than in here. With our limited view angles (8 directions plus up and down) you have to constantly jockey around instead of just following it instantly and carelessly with your eyeballs. Not only that, but in real life things have much higher contrast and brightness, and you would easily be able to see a con even if it was against the ground and wearing camouflage.
It's because you're close to it and it's moving. Your eyes see moving things a LOT better than stationary ones. Camo might work at long range (that's what it was intended for) but up close you could still see it and track it easily.
That said, the same constraints exist with or without icons. If you have a con go below your nose, under your tail, drop below your wing, etc, you lose sight of it. Same as in real life. However when it's on your screen this game (and most games) has a poor quality compared to the real world.
Don't believe the IL2 minority crowd that proclaims "no icons" as realistic. And don't claim that only "experts" would use it. It's an arbitrary handicap for the sake of making things harder (NOT making them more realistic).