Based mostly on some things I've only recently heard, namely the circumstances of Dorn's casting and his late arrival to the cast, I would tend to think Worf was more the extraneous character the writers (and the actor) didn't know what to do with, at least at the start.
It might have stayed that way if Crosby and Yar and stayed on the show.
I think it was interesting that the Yar character wasn't given the happy, utopian life that seemingly most of the rest of the crew enjoyed. She had a very troubled background, and I think the writers would have delved into that a lot had Yar stayed around. I think there could have been a lot to explore there.
It seems it was only with Yar removed that Worf got more development and play. Worf (and my extension the Klingons) may not have become the character he did if Yar had been there.