First of all I think DB can design a good plan to be good at both races but one should be worse than the other.
Can win the Giro? Yes, the TT, the lack of a clearly better climber and his powerfull team can lock the race. Despite the italian climbs are more difficult to control.
After doing the Giro can win the TdF... without a very long TT he has no advantage over climbers, even less to those who can TT and has to hold Andy, Contador and... Froome itself at climbs. RNT and Saxo can send powerfull team too and split the team to help Wiggo and Froome at the same time it's not a logic plan