1. My point remains no matter what happens in the other cases.
2. Some important info
The normal use cases are
1. When Hp of X mod 8 and Hp of X mod 4 are equivalent then PC 1 will require Y attacks and PC 2 will require 2Y attacks to defeat the enemy
2. When Hp of X mod 8 and hp of X mod 4 are not equivalent then PC 1 will require Y attacks and PC 2 will require 2Y-1 attacks.
The scenario you propose is a major outlier where Y = 2Y-1 (Y=1). So that scenario is definitely not the best use case.
It's worth noting that the larger hp something has the closer case 2 is to case 1 in results. As such, I think I picked a fairly representative case (and definitely more representative than the case you proposed).
Case 2 where Y = 2 or Y =3 would be a much better scenario. As it will have the impact you desire while being more reflective of all the all cases for scenario 2 where Y > 1.
Well, no.
So your point is you found a case where the same expected damage per round favours someone with a larger base damage but fewer attacks? OK, sure. If PC2 hits for N hp and PC1 hits for 2N hp, then critters with N + (1 - N-1) hp will fall more quickly to PC1. Since the case resolves down to critters have 2 hits to kill, PC1 inflicts a one hit per blow with 2 chances to hit and PC1 inflicts 2 hits with a single chance to hit.
When X mod 8 == X mod 4, PC1 requires Ceiling( X / 8 ) hits to kill and PC2 requires Ceiling( 2X / 8 ) hits to kill.
When X <= 4, both requires a single hit. PC1 is providing 8 - X overkill. PC2 is providing 4 - X overkill per blow. PC1 takes 5/3 rounds per kill. PC2 kills twice as quickly..
When 4 < X <= 8, PC1 kills with a single blow providing 8 - X overkill <-- note that the overkill is dwindling here. PC2 requires 2 blows and is providing 8 - X overkill. Note that PC2 overkill is now identical to PC1 and any advantage is lost. PC1 still kills every 5 / 3 rounds. For PC2, it takes about 5 swings (2.5 rounds) to have a 91% chance of killing an enemy.
When 8 < X <= 12, PC1 requires 2 blows (and now requires about 5 swings to kill an enemy 91% of the time -- thus 5 rounds) , but PC2 requires 3 (and now requires just over 7 swings to kill an enemy 91% of the time thus 4 rounds).
*ETA*
PC2 has about a equal chance (20-25% chance) to drop his enemy on the 3, 4, or 5th round with 6 + 7 adding up to about the same probability in that 91% window. So it's probably be better to estimate 5 rounds.