You don't want to play magic without any understanding of statistics (and Frank Karsten is my favorite magic writer of all time), but the Bazaar math really only paints part of the picture. Bazaar is the most important card in the deck, but it's not the only card that matters. Powders mean that on average, your opening hands will be bigger and better. Powder makes you more likely to draw all of the best 10-20 cards in your deck, and cutting it for something else makes you more likely to draw the worst 4 (i.e. the last 4 cards you added)
Because it's only useful if a) the exiled cards provide some ancillary value (castable creatures for example) b) your deck relies overwhelmingly on 1 and only 1 card and your deck doesn't rely on 1 or 2 of's to function that you can't afford to powder.
This is because the card Serum Powder itself once mulligans are resolved is a Bone Flute for the most part. If your hand includes Bazaar and Serum Powder it's largely irrelevant. So the reduced over all quality of a hand is marginal because a measure of a great hand and an unkeepable hand is simply whether it contains that ONE card.
Dredge is so far the only competitive deck in Vintage that meets that criteria. There have been Shop decks so bent on having Shop the opener they've played it. In Legacy an example of a deck that can use it is Leylines ... the deck needs 1 card in its opener, Opalescence. The Powder is moderately castable off Sanctum as well.
Powder would actually support your ability to find critical 1-of cards, so I don't think that's a very sensible argument against it unless you need a lot of specific 1-ofs in combination with each other.
The "draw your worst cards less and your best cards more often" thing applies to any deck in the format vis-a-vis Serum Powder. I'm aware that some Shops players have experimented with the card, but by and large Shops players don't run it. If it's such a no-brainer it seems like they should generally be running it, and the fact that they are not suggests that there are downsides to the card that Andy is not really accounting for. The card being close to blank after the initial mulligan phase is only one of those downsides.