PK Starstorm does not use an insane amount of PP. It is by far the most efficient of all the ultimate attacks, and is easily the best among them. Once you get PK Starstorm, Poo basically has absolutely no reason at all to use any other Offensive PSI unless he is seriously running that low on PP, in which case he should not use any Offensive PSI at all, but use PSI Magnet and Lifeup as needed. PK Freeze becomes poor by the end. It is no better than PK Fire at that point. And PK Fire is plenty good early-game. But both are completely outclassed by the time you get PK Starstorm. In fact, PK Freeze is much less efficient than PK Starstorm. PSI Starstorm Alpha will be dealing more damage than PK Freeze Omega to all enemies, while still using less PP. I do not get how it has an "insane" amount of PP, when it is both better and cheaper than PK Freeze. PSI Starstorm Omega uses more PP, but it hits much harder than PK Freeze, and strikes all enemies. By the time you get it, PK Freeze is useless. Basically, elemental PSI is useless by the endgame in EarthBound. And PK Thunder is not elemental PSI; it is non-elemental in EarthBound, which actually makes it more viable in the endgame.
Ness' healing powers are much better than Lucas overall. He has over double the PP that Lucas has, his Lifeup is much stronger, and let us face it -- it is shameful if more than one of your characters go down at once. That is very rare. With Ness, the entire team is basically invincible. He can use Lifeup Omega every single turn without breaking a sweat, and his Lifeup puts Lucas' to shame. He is also the better attacker, with his better SMAAAASH!! attacks and PK Flash Omega. His Assist PSI is also better, with the ability to completely shut down multiple bosses and enemies. Paralysis is overpowered. Paralysis singlehandedly compensates for all of Lucas' Shields and boosts. Ness can also Shield to a lesser extent, and has Hypnosis.