Jigglypuff is almost certainly better than Samus, though; I'd go so far as to say that she has the potential to be one of the highest in bottom tier.
Her aerial mobility is excellent, and is quite capable of weaving in and out of the opponent's space. She has five aerial jumps, each of which give her a reasonable vertical ascension, which makes her recovery quite respectable and variable, a weakness to meteors notwithstanding (her ridiculous ledge grab range helps, too). She has an exceptionally and deceptively good grab range, and though her throws aren't very good at killing, they all do 10% fresh, which makes them excellent damage racking moves. The ability to inflict more damage by reading the foe's DI makes them even better.
Her range is quite mediocre, and her ground game is quite bad aside from her Dash Attack and Grab. You'd be surprised how quickly she can build up damage, though, especially with good reads.
Basically, I view Jigglypuff as a worse version of Wario, Kirby, and to a lesser extent Meta Knight. Since many of her attributes are simply watered-down versions of these high-tier characters, I see now reason as to why she couldn't be higher.
Also: Rest is a rather mediocre kill move, especially against heavyweights, who could certainly survive a fresh Rest around 100% with proper DI.