I like Ahsoka and this isn't the first series to show age progression (it's actually fairly common in anime. Dragonball is an excellent reference. Goku started off as a kid and gradually grew up over many years and we could see him getting taller, filling out more, etc etc.). More than physically, Ahsoka has matured mentally as well. She has learned well from her mistakes and points out those than Anakin is making based on his own feelings.
So far as he has not been made out to be stronger than the Masters. And if people think that's somehow uncommon in SW, it isn't. Feck, look at SWTOR. Consular goes from Padawan to Knight to Master inside a few months and becomes one of the top Force Users of the time. Bane became stronger than his masters (who, really, were all pushovers except Kas'im). It's a common occurrence with Main Characters that they tend to become as strong, if not stronger, than their teachers.
However, Ahsoka has not displayed any such sign of being an uber-powerful Jedi. Strong? Yes, but that comes with being a major player in the continuing story. As far as that goes, she will become as strong as she needs to be given the situations she is put in, but may never reach Anakin's level.
As for Darth Maul. Well look, we've had Sith who've survived as a head in a jar. Maul with robot legs isn't that big of a stretch.
Actually it is 3-5 years. But you do make a good point.