Yes, YP is weaker than Delver and much more so when you don’t even want Probe in your deck.

I just prefer to have cards that are more coherent in my strategy. For example, boarding in Spell Pierce to counter Expedition Map and Amulet of Vigor jives well with the counters that I already have in my deck against Tron, whereas the random Blood Moons operate exclusively of the over-all strategy. Costing three can also just put you behind where you need to be while Spell Pierce can keep you in the game and stop things from ever potentially spiraling out of control.

Spellskite is just something that I’ve never really wanted in this deck. Twin is just a grindfest, so having something in play that they can K Command then combo seems weaker than fighting a counter war where they need to commit a 3 or 4 mana spell to the stack. It’s strong against burn, infect, and hexproof, but the first two are positive matchups and Hibernation is a much bigger blowout that you can topdeck and have it be relevant against hexproof.

Both cards are respectable options that will win games, but I feel like my choices give me better odds.

In my experience, YP has been strictly worse than Delver. You really feel the extra mana in the cost, and the reason that Delver still has a home is the evasion. You also are only ever getting multiple tokens out of Pyromancer when you have 4+ mana without Gitaxian Probe- which doesn’t make the cut anymore- and at that point I’d rather just jam more Gurmag Anglers- an idea that I’m not entirely against. They key difference there is that Lightning Bolt, Electrolyze and Kholaghan’s Command really get YP.