I can't speak for where Mr. Safety is coming from, but when I differentiated between an all-in approach and grindier approach, it was based on these distinctions:
1) Fetchlands and basics vs rainbow lands. The first means better Bloodghast recursion and more resilience to mana denial. By mana denial, I mean early Blood Moon (Dragon Stompy) or a turn 1 counter followed by Wasteland (Delver). Wasteland on its own is not that dangerous if we already resolved a discard outlet, but the 1-2 punch of counter+Waste is devastating. Less than half of opening hands will have Caverns, so it's a risk.
2) Being fully-committed to the madness/graveyard plan. The less explosive list has a better shot of having a transformational sideboard into a plan B.
I used that in my old BG Vengevine madness deck 7 years ago. It was a more effective way to dodge gravehate than boarding in reactive answers (e.g. boarding out Bloodghasts, Buried Alive and Vengevines for Dark Confidants, Thoughtseize and Abrupt Decay). It was hedging between an explosive deck and a fair deck, the way Survival lists used to.
The explosive plan can't pull that off. There are too many cards committed to the main plan and a lower land count. You're not winning a fair game. That means the sideboard needs to be answers to gravehate, instead of a plan B. Dredge has the same problem. It's hard to win game 2, not knowing which hate to board against. If you bring in Nature's Claim and they have Surgicals, awkward... Still, this has more diverse threats than Dredge and should be harder to hate out.
3) Threat diversification into cards that are both enablers and alternate win conditions: e.g.
Lotleth Troll,
Carrion Feeder,
Cryptbreaker. These cards don't help you get the explosive turn 1 Hollow One starts, but they play dual roles of enabling your free guys or also threatening to win the game on their own, even if your graveyard is hated out or Hollow One takes StP. Cards like that reduce your turn 1 explosiveness rate but increase your chance of winning through spot removal or a Tormod's Crypt.
I found the threat diversification angle very useful in my old Vengevine Madness deck, but that was before
Hollow One. That was also in a metagame full of creatures (Maverick, Stoneblade, D&T), where having the grow guys grinded out wins. I have yet to test whether in 2019 you win more matches by having more explosive turn 1s or by hedging with alternate win conditions. In this meta, explosiveness is probably the right call.