just my personal opinion amalgamated from reading random news about smash development/nintendo in general and looking at game code, but plenty of things about brawl scream 'this was totally gonna be a competitive fighter, and at the last second we had a change in design direction and added in **** to make it more accessible to everybody'.
For instance, Brawl hitstun has the exact same value within the code as Melee, but it seems like something was slapped on near the end of development to shorten the length. Likewise, tripping seems like it wasnt adequately playtested (see: single naner lock infinites), and theres evidence that diddy would have an ice climbers type situation with dixie as his partner (their down-b being the ability to switch who's the lead, rather than bananas).
Not to mention when Brawl came out was right as nintendo started going crazy casual-friendly...if it was released 6 months earlier it probably wouldve been before the switch (and thus more melee-like, as it was at E for All 08 (i think that was the setting for gimpyfish's old 'first impressions' article)), but 6 months later it probably wouldve been more polished but way more scrub-friendly
Not necessarily related to competitiveness but my guess is that they decided to add in jigglypuff/toon link/wolf/sonic very late in development as well
jiggs/tl/wolf are the only 3 characters not to play a part in the subspace emissary and are absolutely dead last in the character id list with a significant gap between them and everybody else (except maybe the third parties, i cant quite remember off the top of my head)
sonic also only comes in right at the end out of nowhere in a sort of deux ex machina moment without any prior presence
not to mention half his moves look alike/feature him curling up into a ball, which seems to me like they put him in while running out of time
and the whole 'mention a delay the same day we reveal his entrance' deal