The most important thing, I think, is: the stunt/power has to fit the character concept. The conviction stunt is basically made for the true believer type of character, it wouldn't sit right with me to just have any character take it just to minmax his fighting capability. Think of a character concept first, then look at the stunts and powers that would fit the concept or create your own to get a character that represents this concept.
As others already said: if he wants to use athletics as an attack, he is going to need enough space, so crossing a zone should be necessary to use this stunt. And if he wants a shapeshifting ability, I would not allow him to use that stunt while shapeshifted. Fists is the skill that represents how you use your own body as a weapon, so if he shifts into some beast, he should use fists for any attack. Plus, he gets to shuffle around his skills anyway, when he shifts, so why would he need a stunt then?
The idea behind the fists for dodging stunt is, that you are trained in martial arts and therefore your fighting experience is rooted in your fists skill. You do not dodge a bullet whit athletics, and you don't dodge a bullet with this stunt, it just represents, how well you can position yourself, how good you can keep track of everyone involved, note if someone is trying to attack you and react in time, that sort of thing.
If you want a speed/athletics kind of character with shapeshifting, you could try a werepanther concept or something like that. Basically you take the Werewolf template and change it a little. Remove Pack instincts and replace it with cloak of shadows to represent the stealth capability of the panther. Again, you can shuffle around the skills, so there should be no need to take a stunt to attack in shifted form. Echoes of the Beast might provide stealth and/or athletics bonus for running, so if he really wants to the shifted form would create a benefit to the athletics for attacks stunt.
