Okay. For starters, Kubiak has shown a lot of promise as a coach but he's also shown some chinks in the armor. He's got this team motivated and is changing a losing culture which is INCREDIBLY hard to do. So said, you can still see holes in some of the playcalling (find me a fan that doesn't have complaints with his/her coach's playcalling) and his clock management will make you scratch your head sometime. So "great and all wonderful?" No. Solid and showing lots of potential for the future? Yes.
Domanick Davis / Williams a failure? Wow. Okay, DW was probably best suited to being a third down back but toted the rock as a number 1 RB for three years and broke down under the load. DW had 3195 rushing yards, 1276 receiving yards, and 28 TD's in his short career. He's still the Texans' all-time leading rusher and most Texans' fans have a soft spot in their heart for the man who, for a time, was the Texans' most potent weapon. Heck, if it hadn't have been for DW catching all of those passes out of the backfield then David Carr would have had his confidence shattered much, much earlier. DW may have left a bad taste in some folks mouth with regards to his knee, but he was in no way a failure. Furthermore, Kubiak was in no way responsible for DW's knee or contract and saying that Kubiak put his faith in him is, in my opinion, inaccurate at best.
Ahman Green was brought in as a short term solution (yes, a stop gap) at running back and his contract is built like many are these days - essentially a 1 or 2 year deal with lots of "funny money" in the back end of it that AG will probably never see. Now, calling a five-time Pro Bowl selection with 8640 rushing yards, 2744 receiving yards, and 69 TD's a failure is laughable. Furthermore, AG is known as being a fantastic pass protector and you will never be able to tell me that was not a huge factor in why he was sought by our GM and HC. He's been nicked up for sure. But he's also been the only back we've had who's had ANY measure of success running the ball. He'll be back again this year and I'm sure that he'll be productive. I'm also sure that he'll miss some more time because he's older for a RB. Does that make the AG signing in the off season a bad one? No. I'd say not. What was a questionable decision was going into the season with only Ron Dayne and Samkon Gado behind him.
This one to me is the funniest. You make it sound like Kubiak and Smith have been laboring with the RB situation at Houston almost as long as Chicago has been trying to find a QB. Ahhh yes. The 2 years of woefully inadequate RB play. Dude, in case you haven't noticed, they've remedied the woefully inadequate QB play, TE play, OL play, DL play, etc. They had soooo many freakin' HOLES on the roster that they couldn't address all of them immediately. Based on that, I'm willing to give them a pass (albeit a short one) on the RB play. So based on what I've seen out of him and Rick Smith I would be inclined to say "Heck yes, he does have it in him to find a running back." And I don't think it will take forever, either.
Uh... until Ahman comes back or we can draft / sign someone next year the answer is a firm "Maybe." Sometimes Dayne is good for two yards depending on how many D-linemen he bounces off of when he falls.