I would argue, however, that the difference between something like a
Young Pyromancer and a
Delver of Secrets is when they gain value from a spell.
If your opening hand has 3 instants, a
Young Pyromancer, and 3 lands, then Pyromancer is for sure getting 3 triggers that game provided it doesn't die.
Delver of Secrets, on the other hand, would not necessarily flip in this same position. In fact, delver would be at a
disadvantage in a starting hand with 3 instants because it would have fewer cards in the deck to trigger it.
I also think that Delver's randomness is slightly different from other card's randomness. Delver always
feels like a coinflip in the sense that you don't know whats coming next without TOD manipulation. "Bad luck" is a feeling that can be put front and center with
Delver of Secrets. To be fair, any magic game can be ruined by so-called bad luck, but it's a lot less apparent in the course of a regular game. Not drawing an instant for 3 turns after playing
Young Pyromancer is arguably almost as bad if not worse than not flipping a spell for 3 turns off of a delver, but since Pyromancer has a cast trigger instead of a upkeep trigger, the player isn't constantly reminded of not having their engine online. I don't have much of experience with Scary Pterry, but I think he probably falls into the same camp as pyromancer.
Basically, Delver randomness feels bad, man.