to start, I want to say that I'm using numbers from Frank Karsten and extrapolating from there, in addition to basic combinatorial work that anyone can do themself in excel.
The london mulligan has people discussing playing dredge without 4 serum powder, and even testing it during the mtgo test period and in paper events with the new rules. In my opinion, playing dredge without serum powder is a mistake. the following is an anecdote and then some numbers.
Anecdote: I played in TSI this weekend with dredge under london rules. List was similar to @ChubbyRain and others recent lists, with hogaak, force of vigor, and field/salvage as only nonbazaar lands main, playing ghast and ichorid over narcomoeba. I went 2-4 in games where I mulled to 4 or less and 8-0 in games where I kept 5 or more cards. I sleeved up a list with powders over the 4 worst cards for an eternal weekend trial the next day, but it ended up not firing.
Dredge probably has a better win rate when it keeps 2-4 card hands than any other deck in any format with such hands, but given how often we mull it leads to a significant portion of our game losses. But first, the math if all we care about is finding bazaar:
Vancouver Mulligan, no powder has an 86.5% chance of finding a bazaar if you're willing to mulligan to one card, discounting the scry. miss every 7 games.
Vancouver Mulligan, with powders has a 94.17% chance, a miss every 17 games, again discounting scry.
London Mulligan, no powders, has a 97.2% chance to find a bazaar, a miss every 36 games.
London Mulligan, with powders, has a 99.3% chance to find a bazaar, a miss every 143 games.
(As a refresher, the powder-London interaction is that you put back the number of cards as if you've kept the hand, exile the hand to powder, draw that many, then have the option to mulligan to another 7 if you don't like what you drew and keep going.)
of course, bazaar isn't actually everything, and mulling so low that you don't have the ability to keep counterspells, hollow one, unmask, cards to pitch to counterspells/unmask/FoV, or lands to trigger ghast in hand after you activate bazaar, or having cards to discard as you dig for these things. This is my primary point in favor of the continued use of serum powder- not the 2% increase in finding bazaar, which is significant, but the average hand size at which you find bazaar.
Playing serum powder increases the average hand size you keep by over half a card. The proportion of hands kept that are 5 or more cards goes up over 11%, from 78.2% to 89.6%.
By the mulligan to what will if kept be a hand of three Powder-London has a higher chance of finding bazaar than pure-London has if willing to go to one. London has to be willing to mulligan to 2 to have equivalent odds to Vancouver-Powder, while London-Powder only has to be mulliganing to 4 to have chances better than what dredge has had under the old rules. We are of course going all the way down, but I think these are useful comparisons.
This glosses over a few bits, such as assuming that what you powder from your deck is a cross-section of its components and thus doesn't change its strength, but this isn't the case. Powder exiling non-bazaar cards leads to a higher proportion of kept hands with double bazaar, for example, and there's some other changes once you've mulliganed and have some choice over what you're exiling(this probably also changes the powder math slightly as you can put excess powders back before powdering the hand). This is all hard to sim, as is figuring out exactly how much higher win rate you get with double bazaar over single and stuff like that, so maybe another time.
to sum up main points, powder is still worth playing in dredge, partially for the raw percentage chance of hitting bazaar but moreso for the larger portion of games in which it allows the player to keep a hand with enough cards to do something.
does anyone have a large dataset of dredge starting hand size vs game win rate?
Then, a question follows, are there particular plays in particular decks or matchups that you believe demonstrate a Vintage “maturity” and are a tip off that someone is evincing particularly excellent gameplay?
obviously i will mostly be talking dredge in my examples here
so the basic level of dredge play is simple enough to describe. mull/powder to bazaar, don't miss triggers, activate bazaar on upkeep in response to ichorid to find (more) black creatures to exile it. sacrifice your bloodghasts before playing a new land, attack with your creatures before sacrificing them unless the sacrifice involves a combat-relevant dread return. basic use of cabal therapy. for the most part this can be considered mechanical play.
the level of play past this involves knowing when to break those rules. when to keep a non-bazaar hand, or mulligan a hand instead of powdering it. when to not activate bazaar on upkeep, or to skip dredging for draw step, because you only lose if your opponent has ravenous trap. sacrificing some of your creatures to get zombies before attacking with the others which will give your opponent the opportunity to break bridges. advanced use of cabal therapy.
the third level of play is when you do the basic line anyway after considering the alternatives
so in dredge, here's a simple example of the different things a player might consider, and do accordingly: your opponent is at 18, tapped out, 4 cards in hand, no blockers. after bazaaring, you have a bloodghast in play, another in the graveyard, as well as 2 bridges, a therapy, a dread return, and a flame-kin zealot, with a land in your hand, land drop remaining. the mechanical play is simple: flashback therapy naming force of will off the ghast, play the land, sac the 2 ghasts and a zombie to dread return FKZ and attack for 18.
now, the level above that: it's possible their hand contains misstep+force+blue card, in which case attacking with the ghast precombat nets you damage for the same resultant board(5 zombies). if you have a strong enough read on your opponent having those cards in hand you might attack for 2, then cast therapy, play land, cast dread return.
past that, you might realize that your opponent doesn't have a reason to force a post combat dread return the way they would a pre-combat one(this is often the case when it's just putting power and toughness on the board and not, say, iona). as a result even if you think they have the misstep+force+blue card you decide that the 2 cards in their hand are worth more than the 2 damage and go for it precombat like anyone playing dredge for his second tournament ever would.
there are no synergies with Ichorid as they trigger on upkeep, and Bloodghast can complicate matters if you need to play a land to cast Molderhulk.
it synergizes fine with ichorid by being a black card. the complication with ghast is optional, as bloodghast's trigger is optional, you can leave them in the yard if you need the creature count and just get them off the trigger from the land molderhulk gets
to use stoneblade as an example, I don't think there's any reason to build a deck with stoneforge in it that doesn't just turn into a variant of the stock jeskai lists. equipment are also worse in vintage than in other formats due to everyone packing artifact hate at much higher frequencies.
that's an object level case against a particular deck, and while obviously similar explanations could be made for most others, it's not entirely satisfactory. before survival put up results similar arguments could have been made to dismiss it.
to use your classifications, 5 tier 1 decks seems about as many as can be expected in most formats, though there's not as many tier 2s as others have.