I have 2 4-1s in a deck without dread return and with 4 Hogaarks. It’s not pitch. It doesn’t run bridge. A free 8/8 is pretty good without extras honestly. I was testing a minimalist hypothesis by cutting cards like narcmoeba. You don’t need four but the fact that it pitches to Force of Vigor, Ichorid, Unmask, and Contagion/Shoal means the diminishing returns of running 4 are virtually nonexistent and this argument is pretty irrelevant. Play as many as you can fit.
I think you're thinking about this backwards. My concern is not that I'm going to have too many Hogaaks and be unable to find a use for the 4th one. My concern is that slots are valuable, and the 4th Hogaak has to pull its weight for me to choose that card over an additional Mindbreak Trap or the one-of Gitaxian Probe or the Strip Mine or whatever the best card I could run would be. If 3 Hogaaks gives me a certain level of ability to close the game with the Dredge plan, the 4th has to make a serious contribution beyond that in order to justify itself.