I don't even think customs is required for him to compete, although I think wizard drop kick's utility is a really big boon to him.
His customs obviously help, but I feel like it's more him edging himself towards low high tier or the top of upper middle.
Anyway, I'm wondering whether Lucina would be the worst character in the game now. Let's ignore Marth here (he could still be a tier better than her, but the gap is smaller than before thanks to Lucina's widespread damage buffs).
Dancing Blade being back is all sorts of amazing. Fair and down tilt to dancing blade are very clean 20%+ combos that work a lot and force a terrible position onto the opponent. It's transcendent priority, and she's one of only three characters (I'm aware of) with transcended tools as diverse as she has. With slight damage buffs on her down tilt and fair, both notable pokes, she would have slightly more safety on shield with them too, potentially being on parity with Marth's tipper spacing with her own in literal frame safety.
Forward Tilt and Jab having cool down buffs ups her capabilities to wall ever so slightly for sure. That 3 frames off jab could make the dash grab or dash db (I'm thinking its working on Marth so yeah) a lot more accessible as a mid range trap.
We all know Forward Smash is godlike.
All things considered, I think her game plan may now actually have solid and logical "winning" choices; the potential for more rewards from hit confirms, reads or punishes and that dynamic likely being enough to force respect from most opposing characters, something she needed more than everything else.
I guess all in all I'm thinking she will now play much like the passive defensive style that Marth had in Brawl (although later in the game an aggressive style or mikeneko's style were the most potent). Moves which can be safe, can restrict opponent's movements, the snowballing effect of dancing blade for traps and positional domination and perhaps all that's needed to get forward smashes through punishes that likely become more available. (WALKING SUDDENLY BEING USEFUL!)
I genuinely rated Lucina (and Marth) towards bottom of the cast in the last patch, and with everything considered now, I can't say for sure where they lie. A lot of match ups for the characters could in theory and hopefully soon in practicality start looking a lot better than before.