Dark Souls PC is a bad port. The KB/M support is abysmal and totally broken. They put so little effort into the port that it's easy to assume that they were forced to do it by the publisher and simply wanted to cobble something together and ship it.
As far as the game being designed for gamepads it's undeniably true. That said there is nothing about the gameplay itself that wouldn't work properly with KB/M if any effort had been made to support it at the basic level. I'm slogging my way through the game slowly using KB/M and it's certainly doable with some tweaks to mouse sensitivity, but it's an aggravating experience beyond the inherent difficulty of the game itself. Great game, awful port.