A "Wall" spell isn't on par with the most powerful attack spell we ever see. There are clear limits to conventional weaponry when compared to things created by the planet's spirit energy. This is like Operation Mi'hen trying to brute force victory with technology. Meteor simply isn't gonna disintegrate due to the fact it's got some sort of gravity magic perpetually holding it together and keeping it from breaking.
I think you guys are debating a technicality, it's just that Makoeyes keeps conflating an instance of the spell with the ability to re-cast it. You've actually both pointed out that conventional weaponry absolutely could
disperse both Sin and Meteor, given an appropriate yield. The core problem is that its caster remains alive to undo the damage. Sin is actually a good comparison, because the airship demonstrates that, actually, Operation Mi'hen would've gone just fine had the technology been enough to actually obliterate Sin root and stem. Drop Sin in our world and it wouldn't last five minutes. They just didn't have that level of firepower. In Meteor's case; Sin's caster is literally inside the spell, whereas Sephiroth is not.
So, all told, you have to give Shinra credit for trying, just like the Crusaders in Operation Mi'hen. And when you don't have any real plan B, sabotaging an Operation Mi'hen equivalent when you don't even know for sure that it will fail is
kind of a dick move on Avalanche's part. In both cases, convential methods could well have instituted a temporary reprieve. After all, Operation Mi'hen theoratically could've destroyed Sin forever, had the power been there.
I disagree with the idea that there's a fundamental disconnect between magic and conventional weaponry. If anything, Final Fantasy pretty much always eschews that gap, as I just explored. Conventional weapons blow Sin's arms off, they destroys Sephiroth's barrier, the Ragnarok sexually penetrates the Lunatic Pandora's shield, the fall of Bahamut threatens Rabanastre's paling etc etc. I mean, Final Fantasy VII's entire planet is basically a magic rock just like Meteor. We're told at length that it can be threatened by physical wounds but can restore itself--
to a point. In other words, so long as its "caster" (in this case, the Lifestream itself) survives.
Sephiroth: Once the Planet is hurt, it gathers Spirit Energy to heal the injury. The amount of energy gathered depends on the size of the injury. ...What would happen if there was an injury that threatened the very life of the Planet?
[snip]
Aerith: An injury powerful enough to destroy the Planet?
TL;DR:
Can mundane weapons kill a big magic? Yes, absolutely, plenty of evidence.
Will big magic stay gone forever? Highly situational.
Do Shinra get brownie points for at least trying? Probably.