Exactly! The main disadvantage i see in keyboards is ergonomics. Not only do you need a good keyboard, you also have to get a good chair and table at the correct heights to prevent pains in the arms/hands.
A controller usually (you can get pain with a controller too) reduces pain because the ergonomics are designed to fit in your hand, and it's easier to find a comfortable position.
When i play, i use the D-Pad. For it's price, my Logitech F310 (Yeah Eulogus, we have the same controller) has the best D-Pad i ever used (tried PS2-4, Wii, Wii U, Xbox 360, Gamecube).
The D-Pad is very well-placed, it gives a soft feeling that allows pretty fast inputs (all the other ones feel very stiff, Playstation is the best of those).
With a keyboard, you can get almost instantaneous inputs, my brother can't play his rhythm games without one due to the speed required. He tried to use a controller, but the time needed to go from one input to another, combined with simultaneous inputs not covered by the diagonals, giving him a handicap.
Before i gave up with fighting games due to not having a wired connection, i always ended up as a masher, using characters that hit you 3 times and KO you. Yeah, i was that guy with the horrible connection who used Utsuho and Ganondorf.
A keyboard is godly for those combined movement inputs to launch an attack.