I think the bash/knockdown 1h weapons are not 0 slot because of their advantages over 1h swords. Cut is weaker than bash, and 1h stabs are not so great even on thrust-focused swords. With low wpf/ps a blunt weapon will do loads more damage than a cut weapon, especially against heavier armors.
Even if your strength is low and your % chance of knockdown is tiny, it is much better than glancing constanstly with a cut weapon.
With 0 ps and 1 wpf in melee, I glance all the time with cut weapons. With a pierce or blunt weapon I can get kills that surprise both me and my enemy.
I'd like to see the light spiked club and spiked club go 0 slot, with higher upkeep. Since they are pierce they can't knockdown, and both are much weaker than the 1h pick weapons. They are about as strong as many of the 1h swords that recently got changed to 0 slots.
I have rarely seen any hammers or pick axes on NA servers. As a backup people back the new 0 slots or a rondel dagger in most cases.