"Jumpman, the greatest travesty of the PT was those ten years when Anakin is a cute boy and now he is a whiny teenager, what happened? Lucas does the correct thing with TPM and makes Anakin innocent to throw the viewer with preconceived notions that Darth Vader was always bad. But AOTC, begins, and he is a different person, and the viewer is supposed to assume he is has gotten arrogant, just like we should assume he is great friends with Kenobi, just like we should assume Palpatine & Anakin have developed this great relationship behind the scenes. The starting of AOTC makes the viewer assume alot has gone on in 10 years, I say, "SHOW US THIS ON SCREEN!!!!"
Yes, Episode II makes the viewer assume alot. And it's a risk. And see, this is why I can also see a version of the Prequels with Anakin as a teenage in Episode I. But, as you said, Lucas does the correct thing with Episode I and makes Anakin innocent to throw the viewer preconceived notions that Darth Vader was always bad. But, I also feel you loose alot of you make him that age in Episode I. The viewers preconceived notions would still be there if he was a teenage in that film.
But, I don't think the assumptions are hard to pick up on or figure out. But, it does merit your statement of show us on screen. I think he does enough of it in Episode II...which is mostly through dialogue if you can believe it. I think he more than makes up for it in the first hour of Episode III, with the likeablity factor, the Palpatine relationship factor, and the friendship between Anakin and Obi-Wan factor.
But as you say and some others, you felt it was too little, too late. I just don't personally feel that way but I see what you're saying though.