How can people assess unconditional removal for one more mana as strictly worse than 5-mana removal that probably can't kill their 5-drop? I get that blocking is the way to kill things in this set, but even with the whip it's easy to read and still requires setting up.

Sip all the way.

No one said anything about strictly worse.

That said, the difference between 5 mana and 6 mana is often 2 turns, if not 3 (it's pretty rare that you hit every land drop on your first 6 turns). So true, whip may not be able to kill their 5 drop without help, but by the time sip can kill that same 5 drop, that 5 drop might have killed you.

Instant speed is also pretty damn relevant in a format full of combat tricks and auras.

Your first statement ("I'd pick two," etc.) reads like you'd pass hemlocks until you got a 2nd whip. I'd say that's a fairly aggressive preference.

This is an 18-land limited environment. I don't think a land is a two-turn difference in a black deck running sip.

Also, you're generally tapping out in this format, so keeping mana open to cast a meh combat trick is already a losing strategy.

EDIT: Well, OK, you're not always tapping out in this format, fine. But the grindier decks--ones that want sip--don't mind the tempo loss from sorcery speed unconditional removal.

Drafted last night. Took half the Sips I saw. Took none of the lashes I saw. Dropped zero games.

I don't think it's a contest. Whip is fine if you land-go, leave your mana open, and stop someone from voltron-ing a threat. But that's the only time I'd call it situationally better--and that's a strange "better" because it implies you're playing a heroic deck that doesn't have a threat by the time you've hit your fifth land drop. Otherwise, lash only removes a bomb if you two-for-one yourself while blocking or manage to catch a heroic dude before they go off. One card to kill anything is almost always better, even if it only costs one more.

And I just won a draft with 2 whips and no sips.

Anecdotal evidence proves nothing.