most people usually complain about single one-handed weapons being useless. You might be overvaluing the accuracy bonus
Through most of the early game on Path of the Damned, most of the enemies that are going to give you trouble are going to have Deflection scores that are a good 30-40 points higher than your Accuracy. When half of your hits are dealing zero damage because they miss, and only 10% or so actually deal full damage, having the extra 10 accuracy constitutes something like a 30% increase in actual damage - if you have the one-handed talent that converts Grazes to Hits, it's closer to a 50% increase.
Even when you aren't at an accuracy disadvantage, it still works out to about a 20% overall boost, closer to 30% with the one-handed talent.
It might not be better than a different style, depending on the situation, but it's definitely not useless.
the armor damage reduction really should have been percentage-based
Nah, percentage-based damage reduction is a horrible game mechanic, unless it's used in conjunction with other mechanics.
If it's
just percentage-based, then the best weapon in a given situation is the best weapon in
every situation, because it's simply a matter of which produces the best overall DPS. Flat reduction generally leads to much more interesting play, because you can have, say, weapons that deal high amounts of raw damage to low-armoured enemies, that are basically useless against heavily-armoured enemies, weapons that are the opposite, weapons that strike a balance in case you're fighting a mix of enemies, etc. I don't know if I feel like PoE managed to really get that exactly right (and on PotD at least it's definitely skewed toward high-DR enemies, making the faster/weaker weapons pretty poor), but they had the right idea, at least.