Darth Maul vs Vitiate's Sith Empire
The meaning of "deadly" is the ability to cause death.
Darth Maul is proof that the Sith are deadlier than ever.
Therefore, Darth Maul's ability to cause death is higher than the Sith have ever possessed.
But note, this quote isn't restricted to singular Sith. It encompasses any instances Sith have wielded the ability to cause death, meaning amped characters are fair game, as well as the Sith faction as a whole, and also instances when the Sith have owned superweapons.
So who wins between Darth Maul and Vitiate's Empire, given that the former's ability to cause death is higher than the latter's?