[The Might]

"As for the longer road: we cannot afford the time. We might spend a year in such a journey, and we should pass through many lands that are empty and harbourless. Yet they would not be safe. The watchful eyes both of Saruman and of the Enemy are on them..."

I think here you have the problem of seeing this from 2 totally different points of view.
In my post above I talked abut this possibility as an outsider person, that knows well what happened afterwards, while you answered it from Gandalf's perspective. He hoped t pass Caradhras without problems, go to Lorien, then through the Marshes and maybe use sme unknown path to enter Mordor or whatever. Theoretically.
But really would this road I though about have been less safe then all the Ringbearer went through, Moria and the Balrog, Orcs and a Nazgul attacking them from the eastern shore of Anduin, a dangerous passage through the Marshes, Ithilien filled with Sauron's minions and finally the Morgul Vale.

Was this really in the end more safe then going through Southern Gondor to Minas Tirith and then somehow to Mount Doom? I expect Gandalf knew about the Dead so Aragorn summoning them on the way to MT is definitely very likely. Also, the road might seem longer, but would it have really been longer?

And I repeat, I am asking this as an outside observer, and not thinking about what the Fellowship thought.