Allllright, time to get real yo. These are exact numbers.
Sackboys AP requirements respectively:
Total needed each
lvl 1: 100 AP
lvl 2: 325 AP
lvl 3: 600 AP
Now this is exceptionally low, especially for his lvl 3. His lvl 1 has the best/easiest hit confirm in the game in my opinion. (up grab-lvl1 super, no problem) A very decent lvl 2, and the best lvl 3 in the game costing only 600 AP.
Big Daddies lvl 1 also cost 100, and that ish sucks yo.
As a reference point.
PaRappas AP requirement:
lvl 1: 125 AP
lvl 2: 400 AP
lvl 3: 600 AP
Would you say that PaRappas craptastic lvl 3 and Sackboys astoundingly amazing lvl 3 should cost the same amount?
Radec AP requirements:
lvl 1: 125 AP
lvl 2: 325 AP
lvl 3: 750 AP
All of radecs supers cost more or equal to sackboys, decidedly overall superior supers, his lvl 3 costs 150 more AP to get to, and while its still an excellent super it just isnt worth 150 more AP.
Kratos and Raidens AP requirements are exactly the same and unsurprisingly are high cost:
lvl 1: 150 AP
lvl 2: 400 AP
lvl 3: 750 AP
So both of them are a little more balanced because of the absurdity of there AP requirement, which is fine because they gain AP so fast.
In my opinion, the simplest way to balance the characters is an AP movement. As a matter of fact i wouldn't be opposed to Raiden taking even more AP than he already does but thats just me.