Oh I know Samus' strengths. I second her and won one of my local tourneys with her. One of the reasons I have her down there (and I repeat that I don't think a bottom 5 list does justice to the game's balance) is because of her lack of a grab. She has the same problems that ZSS has with it: it's not safe to throw out, it comes out slowly, is easily punished, and her reward for landing a grab stops around 50% (something that doesn't affect ZSS). Another reason I put her there is the general lack of safety on some of her spacing tools. Zair is her best spacing tool by far and there's no argument that it's what keeps her alive in most MU's. When an opponent gets closer to her, though, she starts to have problems. You mention her dtilt and ftilt but they're actually not amazing moves.
Dtilt has just enough endlag for Samus to get punished for hitting a shield with it and has no guaranteed followups. It's nice against people that don't run up and shield immediately but if your opponent does run up and shield, you're gonna get punished. Same goes for ftilt but all those problems are exacerbated by its terrible hitbox design. The change it got a few patches ago that gave it a million different hitboxes really hurt the move. When the opponent is at low percents (0-15%-ish), ftilt isn't even safe on hit if you land the inner two hitboxes against them because of the lack of BKB and endlag on the move. This makes it completely unsafe until percents when the opponent gets knocked into a tumble animation by the closest two hitboxes which is too late for it to be consistently useful.
Her utilt is a great baiting tool because it's endlag is fairly low so Samus can follow up with a jab if the opponent thinks they can punish it. It's also her best combo starter outside of dash attack and dthrow (if she can ever land a grab that is) since it leads into basically any aerial Samus wants but its startup is so slow that landing the move is a chore and, if it lands on a grounded opponent, it can be teched meaning no followups and punished by characters with quick jabs.
Everything else you say is right. Dash attack is good but it is unsafe on whiff and when shielded but leads to uair strings for big damage. CS is what makes Samus Samus. Jab 1 is one of her best tools. Bair is her best kill tool outside of CS and dair spikes. Fsmash isn't actually that great a kill move because the endlag is ferocious and the hitbox is wonky. Utilt is also a kill move on an aerial opponent. Screw Attack OoS is nice but there are characters with better OoS punishes which are also a lot safer than Screw Attack.
Samus has a lot going for her but a lot of her spacing tools outside of zair mean she actually struggles to keep people out of her space and, up close, she's not all that strong outside of her frame 3 jab and decent aerial game. Again, I struggle to consider candidates for bottom 5 because bottom 5 is such a meaningless thing in this game. All the characters I listed could probably be swapped out for another 5 characters (Though I'm not too keen on Jiggly being higher than bottom 5, I haven't faced any amazing Puffs but I'd like to).
As for what Zelda has, I'll say she does have some nasty combos that are started from moves like dtilt, dthrow, uthrow, jab, and nair. The classic one being grab>dthrow>nair>Lkick which works at low percents (0-20%) mostly on heavies which can do a quick 30%. She can dtilt>Lkick guaranteed at mid percents (25-50%-ish), dtilt>jab>dash attack can do upwards of 22% if all hits connect and the DA is sweespotted. Landing nair can be followed up by basically anything including dsmash, usmash, and elevator guaranteed. Landing with the first hit of nair combos into Lkicks as well and can be done consistently out of SHAD. Don't forget Nayru's Love that has intangibility frames between frames 5-11 and does a great job at punishing rolls and spotdodges and does 11% on top of that. Plus, her offstage presence is outstanding since she has one of the safest recoveries in the game. She's got nair and Nayru's Love multihits offstage to catch airdodges and predictable recoveries as well as dair which will spike an opponent even with the sourspot so most characters won't be able to come back when they're sourspot dair'ed.
If you wanna know any more details, here are a few helpful links to our analyses on the Zeldaboards.
Here's our video thread for visual examples:
http://smashboards.com/threads/hyrule-duels-zelda-sm4sh-video-thread.388470/
Here's our data thread for all the raw numbers and some known combos:
http://smashboards.com/threads/the-great-fairy-fountain-ii-zelda-data-research-repository.370698/
And here's one of our best, albeit a bit outdated, guides if you're really curious:
http://smashboards.com/guides/zelda-guide-lightning-looks-good-on-you.115/
hasn't been brought up more. He has virtually no kill power outside of his smashes, throws don't kill at 250%, abysmal grab range, dies at 80%, situational at best specials (except Fire), and has zero options against shields.
