I think this is a good thread and a good question and I like to see all the math here.
I always feel like my thoughts on Serum Powder are completely out of line with the way people talk about it. I think Serum Powder is one of the most powerful raw effects ever printed, uncounterably drawing 7 cards for no mana. Nothing else really comes close to that kind of efficiency, not even Contract from Below.
To me, Dredge has never been the deck that has to run Serum Powder, it's the deck that gets to run Serum Powder. A part of me hears people making the argument to cut Powder, and it sounds to me like saying "Hey they just unrestricted Gush so my deck has a more consistent draw engine, that means Ancestral Recall isn't as important as it was before!" ... it's technically true, but I mean ... don't cut Ancestral.
It's true that the London Mulligan makes Powder less necessary, but it also makes Powder better. Consider that the London Mulligan also makes your 4th Bazaar less necessary, but I wouldn't go cutting it.
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)