I mean, he went to training that move because Ranma had that speed boost so he too needed an upgrade. So, they give him a move that's in itself useless in combat because for one, Ranma can block it, it doesn't even affect humans, 90 % of the debris it causes hits him instead and Ranma is fast enought to block what's left. The ulterior motive for this was to make him a tank. Yes, it made him like that, for that one episode! He still goes down, easy.
And that chi-blast. Yes, made him uberhax. And how many times he uses it after it's introduction? Once in manga, once in ovas.
In Rumiko-land only the main characters can have meaningful upgrades.