He's relatively fast, but not as explosive as most RBs around. And he'll go up against players like that. He can keep up, but on 1v1s with space, he'll get burned.
Maybe he can become a long-term RB, maybe not. But it just isn't that easy, and he also prefers to play in the midfield. I see Mascherano and Alba's examples, but that's two out of several players who made the transition from one position to another.
Let's see though. It's not only to improve his defensive positioning, it's the mentality too. I won't deny he's had a few impressive to decent performances, but that's still a very small sample size.
You guys need to look at the other side of it too. The aim is to improve the team and the squad and while Dani had a few irregular performances, he was still a very important player for us, especially for his contribution offensively, so to speak. I doubt any player in the near future will emulate that, but being a decent replacement and providing the same things to our game would be more than good enough.
Can Sergi Roberto do that? Everyone want him to succeed, being a La Masia graduate, but he has a lot to prove. A lot.
It's a sizeable risk. Let's see.