The existence of other considerations doesn't validate the poor choices that have already been made. I said at the time that putting a vault on a small island near sea level might not be a great plan given the wholly predictable rise in sea levels over the long term.
It was a predictably stupid decision, and the only surprising part is that the stupidity became obvious so early rather than 50 or 75 years from now as more conservative models of climate change suggested could be the case.
I am absolutely in favor of projects like this that are built to maximize survivability of ecosystems in the face of unpredictable change. But you are saying that all risks are equivalent over the long term and it's impossible to choose between them, which I think is an absurd copout.
The reality here is that there wasn't enough money or political will to invest in something more obviously permanent, so we ended up with a shitty system that has started to fail within a single decade, will now probably have to be decommissioned (because the problem is only likely to get worse), and we've got to start over. It's not a total write-off, much valuable work has been done, but it's plain that trying to cheap out on the location was a dreadful false economy.