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.
Before I played in the Challenge on the 8th, I was toying around with cutting Hollow One.
Hollow One is interesting. The pros are obvious. It's a free 4/4 body, and unbelievable in multiples. It's also great in the Leyline subgame.
But I also agree with the point that he rarely is going to win a game by himself without either 1) disruption 2) countermagic, or 3) additional offensive action. And he can massively backfire when playing against Dack.
But I think the under appreciate cost to Hollow One is that does nothing outside of your opening hand. When you are dredging, hitting Hollow One feels really bad. Disruption like Force of Will, Misstep, Unmask, Force of Negation, Force of Vigor also take up the same deck space, but they all directly contribute to the win much more forcefully and immediately than Hollow One attacking for 5 straight turns. that's because they counter the opponent's attempts to stop you or their main game plan.
I've not yet been courageous enough to cut Hollow One - mainly because I feel like I want it against Eldrazi, non-Dack Planesewalkers, and the Leyline mirror, but it's something on my list of things I want to test.
Three countertactics for dealing with it:
a) run max Ichorids. All you need is 7 Ichorid activations unmolested to win with it through Tabernacle
b) run a single Dakmore Salvage or Riftstone Portal. This can allow you to keep an Amalgam around, and attack with an Ichorid for the win
c) Run Dread Return package, and play Ashen Rider to blow up Ichorid or win hastily with Kologhan, etc.