If it's the most unbalanced matchup, and it's <, and there are other matchups that are <<, then there's a flaw in the logic. Just pointing it out
But in seriousness, here's
my opinion:
DK > Jiggs
DK can easily out range and out camp puff. Sure once puff gets the hit on DK, it should be an almost guaranteed kill, but with DK's range, it's too difficult to get that one hit. That, along with Puff dying early (Fthrow or no Fthrow), I say DK has the advantage.
Luigi >> Jiggs
Too easy for Luigi to combo into up-B (or down B) combined with puff dying at rediculously low percents... add to the fact that Luigi is hard to combo for puff since Fthrow sends him too far. Then again, it's not impossible for puff to combo Luigi, but there's just too much going for Luigi.
-Smart- Fox > Kirby
Sure, any random Fox can walk into Kirby's up-tilt and get sent off the edge and be easily edgeguarded, but a smart Fox player should be able to avoid Kirby's up-tilt. Now I will admit... I haven't played this matchup in a very long time, so my opinion may be way off, but that's how I feel this matchup is.
Samus > Jiggly
I know people are arguing over this, with some people saying it's even and some saying Samus has the advantage (and I think some say Puff has the advantage). I as puff have extreme difficulty in this matchup. I do worse against Samus than I do against Fox, Pika, DK, Luigi, etc. (mainly because I know those matchups more). There may be something in this matchup that I am missing that makes it even, but as far as I know, Samus has the advantage. My reasons are basically the same as for DK vs Jiggs (more or less).
Jiggly > Yoshi
After having played Yoshiking's Yoshi today (Sept 8 for you eastern time people), I believe this is a Jiggly advantage. Then again, he did say he just came back from retirement (and I'll be honest, he was quite predictable), but that aside, it still seemed like it was a Puff advantage. Yoshi is way too easy to combo (and mashing the double jump does nothing if the puff combos properly... as every hit can be done before Yoshi can double jump). Both characters have difficulty edgeguarding each other if they recover properly (though it still can be done). Yoshi can combo puff, but it's much harder, as most combos that work on the other characters don't work on Puff, so Yoshi is limited in that sense.
Once again, I admit I'm basing this mainly on my matches with Yoshiking, along with my past experience against Yoshi (which isn't the best to be honest), so this may be wrong as well, but I very much believe that Puff has the advantage.
As for shield breaking... well, this should never happen. If puff gets her shield broken, then that is entirely the puff player's fault. It may happen from time to time, but if it happens twice or more in a match... then there's something wrong with that puff player lol.
As I said, this is my opinion, so some of this may be wrong, but this is what I believe is the case.