Don't you see a giant hole at one point where it has dug through? Doesn't that means it's working?
Anyway, I can see what Nercy means by Yevon wanting to keep control, but this is 1000 years later. You'd think that when Sin first came to be, the Bevelle military or whatever would think "Ok let's work on this super powerful machine to try and combat it." It's not like they would have thought they were being punished for using machines straight away - or at least for the first 100 years.
I always thought them saying that it was too super powerful to use against Sin was a lame plot excuse to have a really powerful ending boss.