No you are missing the point...Konan completely made sure that Obito couldn't touch either sides of the wall because if he phases into Something she wouldve lost sight of him and his chakra, she needed to see him the entire time for the strategy to work, it was also vital that he can't touch anything so sending him underground is really no different than him going underground by himself, which he does all the time
If obito goes underground, weather he is forced or goes willingly, it is the same for the purposes of this stragety. If he materializes while garra has him encased in a sand coffin, he's toast... if he materializes while he's inside a big rock, he's also toast... so what's the difference?
Obito could use kamui as an escape mechanism; sink into the ground, glide undergound a few hundred yards away, then resurface and reset his timer. But if garra can track his opponent's underground (and given his ability to sense kimmimaro's status while he was buried under tons of sand, it seems like he does have this ability), then even that won't work, because garra just follows him and blocks up his space the moment he surfaces.
As far as obito touching stuff... you mean to suck it into his pocket dimension? So that's only going to be fatal to garra if obito manages to suck him up, and I don't see that being a problem for garra, between being able to fly and being able to watch his own back with the eye of sand, obito can't get close to him. Again, obito could use it for defensive purposes, by sucking up garra's sand as it attacked him... in that case, it becomes a battle of attrition, as garra spends chakra generating sand, and obito spends chakra getting rid of that sand.
I was going to say that garaa wins that battle of attrition, being jinchuriki, but I forgot he isn't jinchuriki anymore. So ok, this might work... still seems awfully expensive.
