I'd pick Welbeck over Rooney for a defensive role and as a lone striker where I think Welbeck is a lot better at bring others into play. But as a number 10 Welbeck is a million miles away from Rooney
Right now I'd say Rooney is better than Welbeck in any position, except maybe for the wing positions.
Having said that, I think that Rooney in the no.10 position is massively overrated. I can think of several players in this world who I'd put ahead of Rooney in that role. Mata, Silva, Iniesta, Özil and Kagawa, for instance. There are also several young players like Götze, Reus and Isco who look like they're about to surpass him(if they haven't already).
I still think that Rooney is a lone striker who happens to be versatile and mobile enough to play as a no.10. But he has never been a typical no.10, nor will he ever be. His close control, short passing, link-ups and creativity is just not good enough for that. The reason we've played Rooney as a no.10, is because is because of our style and player material. As long as Rooney participates with goals and assists, as well as working hard, there hasn't really been a reason for us to change our "winning model". But whenever people have complained about lack of fluidity in attack, sloppy passing in the attacking third, and generally being overrun in midfield, Rooney has also been a part of the problem. It's not just our "horrible" midfield that is to blame. Having a player like Mata or Kagawa up front might not result in as many goals, but it's still much better for the rest of the players on the field. I also think it's a necessary step in order to become a power in Europe again. We got unlucky against Real, fair enough. But we still have something to prove.
Before Kagawa came, we didn't have anyone but Rooney to play behind the striker. When Kagawa came, so did RVP. That made SAF change his plans of moving Rooney further up the field. It is pretty obvious by now. At the end of the day, Kagawa already looks like he's around Rooney's level in terms of skills in general, and he's also much better suited for the no.10 role. Why not conclude that Rooney is the elephant in the room by now? Kagawa is 24 and needs more playtime in order to become the star that he is. He also has a much more professional attitude. He deserves the spot now.
That is why I have no problems whatsoever with Rooney leaving. Obviously the main reason is because of his attitude, but I still don't see why he's so important to the team. He's a really good player who most teams would kill to have. But there are several better strikers and no.10's out there. What makes Rooney stand out is his versatility. But in the end, being a specialist might have been better for him. A jack of all trades will struggle to settle in a very specific role when the competition is so vast.