As for your question, we know the damage spreads out over time, considering the nature of Makima’s attack. With the bio stare, it actually takes several seconds before the opponent becomes incapacitated. However, look at the Darkness Devil panel. He’s a Primal Fear who doesnt need blood for regeneration and has the highest endurance in the series.
Alright, let me try give you a scenario.
Look at the scene where Makima takes out 4 opponents with the bio stare, they each drop dead individually right? This suggests that Makima can only focus on one simulated brain at a time. But with the Darkness Devil, instead of taking minimal damage over several seconds like the others,
he just slumps over as multiple faces erupt with blood instantaneously.
This clearly shows that it’s a single attack that spreads out, hence the instantaneous damage and reaction in Darkness’s case. You can even see him slumped in a puddle of blood from how much he lost.