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.
Why should we believe in Captain's Yachts? The Captains were always going places, and they never used any yachts for it. So it follows that there were no yachts, or those would have been used.
Persistent absence of evidence is statistically sufficient evidence of absence. Not perhaps of the impossibility of a thing existing - but that's a different issue altogether.
But that doesn't mean they don't serve a purpose, otherwise why would Shinzon have bothered to have Scorpions on board at all?
For ground attacks? These flimsy craft look and sound just like the thing for flitting barely above ground level and firing the dorsally mounted main weapon at surface targets. Their mere existence certainly doesn't make them space dogfighters or capital ship killers or anything like that.
But the funny thing about the Scimitar
is that it's extremely difficult to figure what she was built for. The Romulan masters of Shinzon seem surprised and appalled that the ship would be used for killing a planet, even though they are fully aware of the thalaron technology, have bloodied their hands in using that technology to massacre the Senate, and would be idiots not to spot its presence aboard the ship. But if the Scimitar
was built to kill Earth, there'd be basically no need for the multiple disruptor and torpedo banks, as a single cloaked planeticide run would be the entire raison d'Ítre of the vessel. The fightercraft would never see action, either.
Perhaps the Romulans had the ship built with the express intent of using it as a deadly threat against the entire planet Romulus, so that Shinzon's little Spartacus revolt would succeed and the military would gain ultimate control of Romulus in the process. A more generic intimidation suite would then be in order, including ship-to-ship weaponry and small craft to subdue resistance and to patrol the streets of Romulus until things stabilized to the cabalists' liking. But surely they'd then install an idiotproof back door in the ship, a system to render it harmless to themselves - and probably also a system to kill Shinzon when he least expects it.