The move that stands out to me most as far as Byleth's ledge trapping goes is up air. It's a great option (high kb, relatively low commitment) for covering a generally strong ledge option. Besides this I don't agree that Byleth's ledge trapping is top tier or close to it. He's got some very strong moves that'll kill early here and that do technically cover multiple options, but all with the same combo of lengthy startup, FAF, and few active frames.
There are two important points here: The first is that ledge jump is an unreactable option. Byleth doesn't really struggle with ledge jump because of his uair, but the range he works in to cover jump is completely incompatible with the range I think most people are imagining Byleth to ledge trap from (this being the range where down angled fsmash will hit a hanging opponent--where side b also tippers and just outside of where he can bully with fair/bair). If the Byleth does want to ledge trap from this range, then side b does hit jump and will even kill--but it has to be from an absolute guess, and guesswork is a characteristic of Byleth's ledge trapping across the board, especially at this greater-than-roll distance.
This is caused by the second point: In a ledge getup situation the timing mixup is usually in favor of the defender. This is increasingly true as a character's startup increases (and as active frames decrease, but this is slightly less of an issue).
Just as a broader note on ledge trapping (I'll come back to Byleth in a minute), I see two distinct kinds of ledge trapping--proactive and reactive.
For the proactive form, think of a Chrom nairing at the ledge before (or as) the opponent chooses an option. This covers unreactable options (jump or ledge drop stuff) while also being safe on neutral get up block (or hitting them outright), and without completely giving up roll (the most crucial option to cover in a ledge trap situation since it's the only one that can immediately remove a defender from disadvantage--a characteristic of every great ledge trapping player like Leo, ZeRo, Samsora, Tweek etc is that this is always the first option they have covered). For reactive ledge trapping think of Peach floating at roll distance with her back facing the ledge. Roll in and neutral get up are fully reactable with bair, a move which also has the added benefit of having no lag (as with Chrom's nair). Lucina is another good example of this kind, but works a little bit differently. She's usually going to force you to pick any option besides roll and then pressure your getup option after you've chosen it, as opposed to Peach who's trying to directly punish your getup (and doesn't usually get punished for messing up).
The best ledge trapping games are reliable and quickly/easily accessible. The best bets here are low startup low endlag moves that can accommodate both proactive and reactive ledge trapping--since you want to ensure you maintain advantage state, cover roll, and threaten coverage of unreactable options. These are the reasons why characters like Peach, Chrom, Joker, and Inkling are so good at ledge trapping.
There are outlying characters here as well, like characters that have moves obviously designed with ledge trapping in mind--Dedede, Zelda, Robin, Simon, and maybe Snake, for instance. All of them have moves that independently cover certain options while the player can then cover something else. oh and there's game and watch, who's just a ledge trapping monster in general.
Anyway, back to Byleth:
Ledge trapping anywhere from roll to fsmash range gives Byleth access to his most deadly options here--but on the condition that they'll require total guesswork. High startup on all of his moves here (side b, fsmash, jump plus fair bair) turns every option bar maybe roll unreactable (unless you happen to be charging fsmash already when the opponent is on ledge, this could be a deadly situation but a relatively inaccessible one). So in theory though side b and fsmash cover neutral getup, jump, and roll simultaneously, the Byleth is going to have to use it proactively (i.e. randomly), but high endlag means a wrong guess (very likely given my second point from earlier) forfeits advantage. (fair and bair can't be used proactively at all because this turns ledge hang safe, and reacting to the startup on these moves equals a free neutral get up).
The best bet for Byleth's ledge trapping will probably be some mix of fsmash range guessing for random early kills and something more reliable--like maybe ledge trapping the way Lucina does, pressuring the opponent after their getup rather than punishing them for the getup (with bair, maybe. it's such a cool move), and covering jumps with uair.
We'll just have to wait and see. the character is new, this is obviously all theorycraft--though from what I've seen of Pink Fresh's play, the ledge traps aren't really there. Maybe Leo will show us the way.
