(It's been a whole year, but if anyone else ever wonders about this question...)
The applicability of DPS calculations
Consider the "zero-shot" problem:
- I have a gun that deals 1000 damage but takes 10 seconds to cool down, with a 1s wait before the first shot.
- My enemy has a gun that deals 75 damage and takes 0.5s to cool down, with a 0.5s wait before the first shot.
Who has higher DPS in a minute's worth of attacks? Who will win in a fight given that we both have 1800 health and never miss any shots? In addition, who spends a greater percentage of their time shooting instead of e.g. dodging?
Consider an analogous situation in Souls, using an approximation of Ben's math against a theoretical enemy with no physical defense:
- The Greatsword deals ~400 damage a hit, with 1.1s before landing the first hit and 1.1 s for each subsequent hit.
- The Dragonrider Twinblade deals ~185 damage a hit, with 1s before landing the first hit and 0.5s for each subsequent hit.
If you have 60s to attack (ignoring stamina), you attack 53 times with the UGS for 21200 damage (~= 353 DPS), and 118 times with the twinblade for 21830 damage (~= 363 DPS).
If you have only 3.3s to attack, you attack three times with the UGS for ~1200 damage, and five times with the twinblade for ~925 damage.
Given that many enemies won't even give you a 3.3s opening, which would you prefer? In particular, for cases where you only have time to get in 1-2 hits with any given weapon due to startup, the discrepancy is even greater, and with a weapon that does more single-hit damage but less overall DPS, you will likely spend less of that time attacking, leaving you more time to maneuver.
Of course, there are many factors at play - the enemy you're fighting, your own skills, and different kinds of damage boosters - but I think you'll find a heavy weapon more effective for a wait-dodge-hit playstyle.
The value of more AR
Note that physical defense is a flat reduction, which means that higher AR has increasing returns: less of your damage percentage-wise is lost when using attacks with higher single-hit AR. Practically speaking, other factors have a much bigger influence on your effectiveness, but if you're using a twinblade, this will be particularly noticeable in certain areas against enemies resistant to slash, like Ironclad Knights (the ones wearing turtle-shell armor).
Hyperarmor and movesets
This is mostly relevant for PvP, but has some applicability in PvE as well.
Frankly speaking, the two-handed twinblade moveset is pretty trash. Hitboxes are small, several attacks have extremely long startup for a "light" weapon, and the only advantage is the high-damage two-handed light combo. The one-handed moveset is actually very excellent due to several unusual timings - for example, the running and light attacks are more delayed than comparable weapons, but the rolling attack has very short startup. Otherwise, it's not too different hitbox and damage-wise from using a one-handed sword.
Ultra greatswords, meanwhile, have very long reach, some attacks with huge hitboxes, enough poise damage to stun almost anything, and the ability to knock down smaller enemies on heavy attacks. You also benefit from hyperarmor, which can get you many hits that otherwise would have been interrupted.
There are some other interesting and fun strategies for a reactive playstyle. For example, did you know that the Great Scythe's hitbox is longer than the Dragonslayer Spear, which is considered one of the longest weapons in the game? With practice, you can duel spear-wielding players by maintaining proper spacing, and attacking when they start attacking; your longer weapon will hit, and their attack will whiff. It's even easier to apply this in PvE: bait an attack, walk backwards, then start your attack during their attack.
As another example, whips have the curious property of being able to attack almost directly backwards with a roll attack if you steer the attack while unlocked. There are lots of fun variations within wait-dodge-hit strategies if you can think beyond rolling backwards or to the side then approaching forward for a hit (backsteps have invulnerability frames in 2!).