Jacob stood in the center of the cyclone, absorbing the huge amount of Blood Vitality from the Beyond Unique Rank assassins. The runic lines on his bones started to light up one after another.
Furthermore, despite all those explosions, he was completely unscratched, and the poison was even less fatal to him despite being a sure kill move against any normal Quasi Legend.
After reaching the peak of the first phase, his control over blood was extremely refined. Despite being diluted and turned into poisonous mist, he could easily separate it as long as he could sense it.
So, in a sense, by blasting off all those assassins, his enemy does him a huge favor. Although it might reveal his ability, so what? He can't continue to hide and waste away all this potent blood vitality, especially after sensing its potency.