Yeah, that makes sense. It's basically
Mastermind's Acquisition + gain 3 life (if they don't kill Karn immediately you -2 again for a 2nd card). It's an expensive line, but less conditional than Helm. I'm not saying Karn is great. Helm just seems worse. Moon has neither postboard.
Helm into Curse demands 1 answer the 60%+ of the time you just have Helm and no T0 Leyline.
If you cast Leyline into Helm into Curse, that demands two answers but is as slow as Karn into Karn-target into Curse (without the benefit of +3 life).
Helm doesn't demand an answer on its own. Vs Delver it's textless and requires Leyline to unlock it. Most of the time you are not prioritizing mulligan to Leyline vs Delver, and a topdecked Leyline is usually better imprinted on Mox than cast unless you also draw Helm, so getting Leyline out opposes the play patterns you would normally take against Delver (prioritize hand with T1 resistor over T0 Leyline, develop black mana, keep as much business as possible). If you imprint another black card over Leyline, you have 1 fewer threat for them to answer. If you're forced to use Mauling as a land to curve out Leyline, you have 1 less interaction for the Delver killing you. Even if you have T0 Leyline, you got tempo but still have -1 hand size. Either way, there's 1 fewer thing they had to answer. It's still a 2-card combo that requires 1 answer for the 2 cards. They can also embarass you on tempo with Petty Theft/FoV on Leyline, making the mana on Helm a waste.
Blue tempo decks do best against decks with dead cards and A+B combos, because instead of having to answer everything they only have to answer certain things. The worst thing for the FoW player to see 30x Tarmogoyf because there are no cracks for them to attack. The power level is uniform and they can't possibly answer everything. The best thing for the FoW player is a deck that has dead draws, Hymns itself, and needs certain cards to unlock other cards, because it makes it easier for their disruption to attack the cracks and tear things apart. From what I saw in the video, some of it was bad luck, but decisions also played into having fewer relevant cards to cast and that meant the blue deck had to answer much fewer things, which is exactly where the blue deck wants to be.
Sure, there is the possibility you had T0 Leyline and they don't have answers for both Helm and Curse and you win. But that seems Christmaslandy. What about the times you have Helms but no Leyline? Or have to lose tempo to cast Leyline to enable Helm? Or had 1 less other thing for them to answer because you had that Leyline, so they end up having answers for both Helm and Curse?
Maybe the line here is just to board out the entire Helm combo and board in all the creatures.
+4 Plague Engineer, +3 Opposition Agent, +1 Bridge, +1 Vault, +1 Spyglass, -4 Karn, -4 Leyline, -2 Helm
This way you're replacing expensive threats with cheaper threats, and each card demands an answer instead of them needing 1 answer after 2 plays. Overloading their answers is what beats Delver.
To some extent, yeah. The bigger issue is Monkey Delver is broken, so maybe you just play to beat all the other decks that try to beat it (and beat the combo decks trying to beat Bant).