Zard, IMO, is way closer to even, if not even slightly Zard-favored. His juggle capability is really strong, as are his floaty-killing abilities. He does get edgeguarded somewhat hard, though. At neutral, he can jab and tilt missiles, and at mid-range, his DD grab game is really strong, although we have zair to help mitigate that.
Yoshi is definitely also much closer to even. It's really hard to kill him or even poke at him with anything. Similarly to Zard, Yoshi is decent at juggling (eggs are pretty amazing at juggling), and he's pretty good at killing floaties.
Kirby is also much closer to even. One of the few chars who can proactively threaten to gimp Samus in almost all offstage situations. He has a really easy time avoiding missiles and zair and getting in, IMO. Our strengths are our weight and CC ability as well as our greater range on our tilts.
Diddy is also much closer to even, IMO, possibly slight Samus advantage if you have really good item play.
I don't really think Samus actually beats anyone you have listed as +1. They're all pretty much even, except for DK (-1). Ganon is extremely scary once he gets in, since he gets confirmed true-combos off both his regular and side-B grabs, similarly ranged moves that can't be CC'd, and great juggle ability. He also has some pretty good anti-tether tech if Samus has to recover low (reverse uair is amazing). Luckily, we can kinda camp him and edgeguard him really well.
DK can easily nair through missiles, CC Samus' ftilt, and juggle really hard. His grab game is extremely annoying when he gets in. Also, invincible ledgedrop upB stuffs literally all of Samus' low recovery options. Zair can stuff him pretty well, and he's kinda easy to poke and combo, but the fact that we can't really reliably kill him until 150+% is also a big problem.
Luigi is actually a pretty weird MU. He can tornado to clank with missiles, which conserves his momentum and lets him approach at high speed with no commitment. We can stop this by missiling his head or zairing. However, he can also punish most of our tilts with WD OoS, and he is pretty decent at comboing us. Fireballs are also pretty good at counter-zoning us. Luckily, he is fairly easy to gimp.
MK has some pretty blatant strengths and weaknesses against us. His weaknesses are that he's very susceptible to CCing and being combo'd, and he's light. His strengths are that he can circumvent his CC weakness with his incredible DD grab game, which is a pretty big problem for us, and he can juggle us for days, finishing off with decent vertical KO ability.
Falco:Samus is even, if not Samus-advantaged. I personally think it's even, or very close to that, in Melee, and there's no reason for a better Samus to have a harder time against an identical Falco. Great OoS answers to shine pressure, great gimp ability on Falco's recovery, hard to kill, can crawl under lasers, etc.
Samus:ROB is pretty even. I play both chars at a fairly high level against other good players of the other char (ROB against Minty and Samus against Rubba Prime). Both of them have good things on each other that are pretty equal in weight. Both can poke and CC each other pretty well as well as edgeguard each other pretty hard. ROB can juggle Samus, counter-zone her projectiles (laser beats everything and gyro absorbs missiles and Charged Shot), reflect her projectiles while approaching on the ground, and he can kill her off the top fairly early. Samus can zair almost anything ROB is doing, she can play for extended periods of time while holding onto his gyro, and she can kill off the top early with anti-air usmash. She can also pressure his shield pretty easily, since he has no good OoS game. His shield is also easy to poke, and he's pretty comboable for Samus.
I personally think Ike:Samus is also a bit closer to even, maybe slight Ike advantage. Missiles can really hamper his QD and he doesn't really have good OoS options, so he can be jab pressured fairly well. What's more, one of his best moves (jab) is easily CCC'd. Offstage, missiles harass him pretty well if he's forced to charge QD high.
DDD I feel beats Samus. I've played a few sets with L_Pag. DDD has a lot of interesting specific strengths on Samus. For starters, he has a very good grab game, which is a major weakness of Samus. If Samus doesn't DI his dthrow perfectly down and away, he gets a CG across the stage. On top of that, DDD is a master juggler. From a distance, Waddles block missiles, and his ftilt vastly outranges Samus'. To top it all off, DDD can very easily edgeguard Samus. He can go out incredibly far, use pretty much any aerial to knock her out of bombs or tether, and then still recovery. Meanwhile, Samus struggles to kill DDD before 150%. Not a really good set-up for an even MU.
I also feel Zelda beats Samus. On the obvious side, you have a land-cancelling reflector, but something more subtle that many people don't know is that Zelda can always punish a shielded ftilt from Samus with a lightning kick. This makes neutral game very grueling because you literally have to resist the urge to tilt her shield, even if you're perfectly spaced.
Samus:Sheik is not even. Forget that Sheilda is actually a thing and Zelda beats Samus, Sheik beats Samus at all ranges. At long range, needles out-prioritize missiles, so Sheik out-zones/out-camps Samus. At close range, Sheik's grab game is devastating, and her throw mix-ups into tipper usmash/uair kill us really early. Our saving graces are our CC ability and our small crawl (we can crawl under needles, and it's essentially a moving CC). Even offstage, we're in big trouble since needles easily knock us out of our bomb jumps and tethers, and Sheik can also cover tethers with bair.
I actually think we kinda body Olimar. We out-zone him since our zair goes through anything he does, and our missiles also kill his Pikmin. Offstage, he's extremely easy to edgeguard if he doesn't go high. The biggest problem we have in the MU is Olimar's juggling.