Melee and 64 are terribly balanced and were balanced by Sakurai alone.
At least with Brawl and Smash for Wii U/3DS he had a team (a relatively small team).
Also:
Of course, I don’t approve all of their proposals right away. There’s no point in making the game more balanced if it decreases the fun factor. To give an extreme example,
I could make all the characters perform similarly to Mario and achieve perfect balance. However, that probably wouldn’t be very fun at all. We work together by making adjustments while trying to preserve the characters’ individuality, then testing out the characters again. I consider all the data the playtesters collect on all the characters and eventually finalize the changes. --
Source
You are literally projecting your expectation/opinion onto Sakurai. "Its obvious X (is to me) so why doesn't he think that?"