For this case of yet another excuse to make a pretty graph, I've defined
lethality as damage-per-second of a weapon divided by health of the recipient. At 1, assuming optimal conditions such as all shots/swipes hitting and the opponent staying within range, the target will die in one second. Below 1, you will need more than that, while above 1 the opposite is the case.
Human weaponsNote: the lucifer cannon primary shot takes three seconds to charge up. The damage is divided over all three, which can also represent players that don't use full charged shots.
Alien weaponsNote: humans in armor are treated as having extra health for purposes of this graph.
Note 2: all hits are chest hits.

It's common sense, or at least it should be that all hits should be aimed at the head. Alien players that constantly target the chest are going to suck terrible because humans are going to seem invincible to everything but advanced maras, advanced dragoons and tyrants.
Alien secondaries were not included (at least not in this revision), but if they were, the tyrant trample would be insanely high and would make all the other parts of the graph look minuscule by comparison.
Also, tell me if my math is horribly wrong, or if there's some other variable to consider when determining lethality.