Vintage Dredge loses to 4 things: mulligans, Wasteland, hate, and faster combo.
Why is Narcomoeba better than Bloodghast? It's better against Wasteland and fast combo, and generally the creature effect is better against hate as well. It also supports a blue package to fight hate and fast combo. Finally, Bloodghast generally requires you to spend a draw on Dakmor Salvage which gives you fewer chances to find additional Cabal Therapy against fast decks or to find your finisher against slow decks.
Why is it important to focus on running more dredgers and dredgers with larger dredge numbers? More dredgers and larger dredgers gives you more speed and consistency to fight fast combo decks, and helps you find key interaction cards like Cabal Therapy as quickly as possible. More and larger dredgers also gives you the best chance to beat Wasteland with slow dredging, or to quickly find key graveyard cards like Dread Return or Hogaak after clearing hate.
Why is Hollow One bad? Hollow One contributes very little when there is no hate, and when there is hate he almost never gets the job done.
Why is Prized Amalgam bad? Prized Amalgam is generally too slow to fight fast combo, his delayed effect is ineffective in fighting through hate (for example, by forcing your opponent to use a Tormod's Crypt more quickly). The fact that Prized Amalgam requires additional graveyard creatures to trigger makes him suboptimal when slow-dredging (for example after Wasteland).
So yes, I think your deck is horribly misbuilt because it allocates a lot of resources and card slots without focusing on actually turning losses into wins. Vintage Dredge is not the kind of deck where you can just throw in "good" or "powerful" cards until you get to 60 or 75 and have a good deck. Narcomoeba is a pitifully weak card, but it's incredibly synergistic with the dredge engine which is why it is almost always a better choice than some other graveyard creature.
Keep in mind that we are undergoing massive metagame shifts and you just got a bunch of new tools that should be expected to help your win-rate with Dredge. If you want to attribute your entire 80% winrate to the strength of your build you have to downplay the importance of these other factors, which I think is disingenuous at best. I'm entirely comfortable saying that an 80% winrate deck is misbuilt because A) I don't believe you will have an 80% winrate with anything like that configuration once the metagame settles down and people optimize their hate and B) I believe with the new tools at your disposal and the relative weakness of the field to dredge you should be scoring even higher. Pointing out that you have a high win-rate does very little to convince me that I have mis-evaluated the build of the deck because I don't believe your build is incapable of winning, I believe it is sub-optimal. So when you say "I have an 80% winrate with this deck" my reaction is "Yeah but what would it be if you took out (what I think are) terrible cards for (what I think are) good cards?" If you wanted to provide some sort of evidence that your build is better than another build you would have to pilot both builds competently and compare their winrates.
Imagine I tell you that a particular build of Survival is the only one being played right now and it has a 58% winrate. How optimal is that build? You have no way to answer the question because you need some point of comparison, a single winrate number tells you literally nothing about how optimal the build is. That's why I am unimpressed with your 80% number - it tells me literally nothing without a comparison to the current winrate of other builds of dredge.
Edit: And of course I've also seen your build in action and Bloodghast has done what I expected it to do, Prized Amalgam has done what I expected it to do, and so on. If I watched it and Bloodghast was way better than the previous 4 times I've tested the card I would update my impression of the optimality of your build.
Edit 2: If you're killing it with this deck, where are the results? https://www.mtggoldfish.com/player/chubbyrain