Other than the fact that they were never needed before, and were never seen again. Fighters don't seem to be in any way tactically valid in traditional space combat, which maybe explains why the Scimitar never launched any of its Scorpion class attack flyers against the Enterprise despite having dozens of them in its shuttlebay.
Your argument makes no sense. Not having seen something before is not evidence of it not existing, its simply absence of evidence. We never saw the space stations Deep Space 1, Deep Space 2, Deep Space 6, or Deep Space 8 on screen, but I'll bet you dollars to donuts they exist in-universe.
We never see the Captain's Yacht on TNG, but the Enterprise-D had one. Voyager had a Captain's Yacht, too. Just because something is never seen on screen doesn't mean it doesn't exist.
And why would the Scimitar need to launch their Scorpions against Enterprise? There would be no tactical reason to launch them. But that doesn't mean they don't serve a purpose, otherwise why would Shinzon have bothered to have Scorpions on board at all?