I actually covered this in my first Push article, here:
http://quietspeculation.com/introducing-push-test/

In that article, I predicted that two-drops, which unequivocally fail the Push test, stand to lose the most from the card entering Modern. I’ve been vindicated, too; Goyf is now the 17th most-played creature on goldfish, appearing in fewer than 7% of all Modern decks.

Three-drops actually improve with Push around, specifically those that die to Lightning Bolt, a card Push has all but replaced. That’s why we’re seeing stuff like Spell Queller so much.

Four-drops require revolt, making them as difficult to Push as three-drops, but the sheer amount of tempo you lose by having your four-drop killed for one mana is so massive that it does not matter whether your opponent needs to wait a turn to figure out revolt. They’re in the same boat as two-drops here, if not in a sinkier one.

Does the revolt requirement factor in to playability at all? Guessing not – your resto angel is pretty much just as likely to be pushed as your birds of paradise, although flash always has the upside of coming in when theres no obvious way for them to get revolt up and then getting at least one turn of value.

This is a great question and something to watch for. But I don’t think we’re quite at the stage where 5 CMC is playable in regular midrange decks.

The 5+-CMC threats that do see play do so in decks that either make them cost 4 mana (via Temple, which is likely to be found by turn 4), big mana decks (Valakut, Tron), or the most dedicated of control decks (UW, which plays 1-2 Gideon Jura). Dismember, Path, and Terminate are still cards, which makes the bar almost impossibly high for creatures that cost a turn’s worth of mana in the mid-game. And besides, why play a midrange deck with enough lands to get to 5 mana when you could play Shadow, which has higher velocity, reversibility, and more as well as a namesake threat with a high payoff than that of most 5-drops in the first place?

Affinity’s continued success seems to indicate that overwhelming Push is a much stronger strategy than trying to dodge it with expensive creatures. Alternatively, finding ways to play high-costed beaters early has a lot of traction—the delve threats have seen increased play for their resiliency to Push, and the GR Vengevine deck from the open focuses on accelerating into Hollowed One (as well as Hooting Mandrills!). The closest to a playable 5-drop we have in Modern is Lingering Souls, which has indeed become better with the format’s slowing. Of course, that’s not a “true” 5-drop, either.

Verdict: Modern has certainly slowed down, but the format’s harsh conditions still require creatures to maintain some semblance of efficiency.

Bolt does more than just remove creatures. Hold off on attacking Shadow decks and they will put themselves within range of three Bolts just so they can save their namesake threat from it. It also kills ‘walkers, and shooting Snapcaster is no joke in a lot of game states. I agree it’s not the “best card ever” in this matchup, but it’s certainly passable against Shadow and therefore in this metagame, which I think is a lot more than people have been giving it credit for.

Games certainly seem slower across the board in modern. It is absolutely nothing like the period of dredge, affinity, burn, and infect hegemony.

It’s definitely a legitimate discussion, I just don’t think we have enough data yet to make that claim categorically, as some writers have (i.e. Ross Merriam).

“I’m holding out for more major event results before also declaring it too strong for Modern”

It might only be rhetorical, but it seemed like you at least considered the discussion legit. Good to here you are on the same wave length 🙂

I also don’t think the deck should be banned currently, as I have expressed in multiple articles (including this one):

http://quietspeculation.com/meditations-format-health/
http://quietspeculation.com/deaths-shadow-hero-or-villain-metagame-impacts/

Which part of this article made you think I believed otherwise?

A few reasons off the top of my head:

1) you don’t need that many kill spells; just playing one or two of the primary removal colors offers plenty in the way of creature interaction
2) Bob is not a playable Modern creature in his own right, as he fails the Push and the Bolt test
3) Souls is overly redundant with the grindy gameplan you’re after; it’s better off spliced into the off-theme decks that actually play it, like Shadow Zoo and Jund Shadow, where it offers additional angles of attack
4) running such a high curve forces you into many lands, lowering the number of velocity cards you can play and guaranteeing plenty of dead draws later. being in blue over white or red already gives you Serum Visions, which helps solve this problem; at that point, you’re on your way to building Grixis or Esper Shadow, which uses its namesake card to overcome the other obstacles slower rock decks currently face
5) this kind of rock deck is durdly enough to struggle against big mana strategies like Tron, rendering it strategically inferior to Grixis Shadow against an open field like the one Modern is known for