Can you not? I’ve played various third person combat games (are they all part of “hack n slash”?) with a mouse just fine. I do prefer controller, but there’s nothing wrong with using a kb/mouse in most of those games. Is Dark Souls control scheme really that bad?
I’m not sure I agree with “tolerating” keyboard. I quite like it over a joystick! The benefit in complex games (like RTS, as you mention) is obvious, but even in most 3D games I prefer the instant reaction and definite axis of WASD over the 360° analog inputs of a joystick. There are not many times I would rather move at 2° forwards-right at a ramping X% speed instead of simply moving forwards at 100% instantly. As for racing or other games that require precise analog inputs, I would generally prefer something that is bigger than my thumb i.e a racing wheel.
That isn’t to say I completely disagree, though! The ergonomics are a clear disadvantage. Most keyboards are not ergonomic for typing, let alone gaming. It would be fantastic to see more gaming-specialised keypad devices other than that one Razor one and whatever Chinese Amazon specials are kicking around. But the keypad format is not something I would want to forego as any FPS I play for more than 20 hours I usually have the entire left half of the keyboard bound to something for quick access.
I upvoted you because this is a great discussion point. :)