Mostly, I think Jak needs an AP boost.
E.g. Mass inverter is one of the slowest abilites in game, you can't really combo off it, and it only generates 5AP + 1AP for each additional enemy.
Or how about the PeaceMaker (UT), it generates 5AP + 1AP for each additional enemy, while Ratchets Similar Ability is 30AP + 20AP for each extra opponent.
Now, I know Ratchets ejects, while you might get hit by Jak Peacemaker more than once, so I think 10AP + 5AP for each additional opponent would be fair. Though as a Jak fine, I would want 15AP + 5AP =)
I think the amount of AP that Sackboy gets on Jam Session needs to be increased, (maybe to 15 or 20 AP) and on his lvl 1, either the startup needs to be decreased, or the range and/or the amount of time there is a hitbox needs to be increased.
I agree that Jam Session needs an AP increase since it has such slow startup and 10 AP is pretty much useless. And yeah, his level 1 could use a range increase. It's one of the worst level 1 supers in the game.
I feel like some of his more difficult to land physical attacks, particularly his jetpack, grabinator grab, and slap, need a buff too. Trying to land a combo with Sackboy is incredibly challenging since characters can knock him away so easily. The AP they generate really isn't enough to make them worth the risk. As it is now, hitting the foe with 3-5 pieces of cake from a safe distance will net you just as much AP as his combos would. So you're better off spamming cake then putting yourself in danger to try and land combos.