Were recon planes used over the battlefield? Yes, of course...
How much could they spot? Stuff moving out in the open, mostly, as they flew low and slow. Makes them vulnerable, though...
Could they report back? Yes, they carried radios, as well as indicating enemy concentrations by circling over them...
Is it "ultra-realistic"? No - just like we have dramatically simplified arty call procedures in comparison to the real world, so the comms with a recon plane is simplified...
And how much of a game-changer are they? In testing, it is one of those things that is not often available and the commander REALLY needs to pick his moment to use. Could just give you the vital clue - or just tell you what your squad leaders already know