Yes, it is.
You will in FFX-2, although, to be perfectly fair, FFX-2 does introduce a severe difficulty drop, so I can understand how one could say that Bevelle's 1000 year-old technology is still weaker than their current stuff, stats-wise. But that would ignore in-game mechanics.
The one on the Moonflow? That wasn't Bevelle's at all. That was an Al Bhed contraption piloted by Rikku for the sake of a kidnapping attempt on Yuna. You can check the script of the conversation she has with Tidus after you defeat it to confirm; she yells at him for blowing up her craft.
Seeing as how Sin is a big giant thing with what is verifiably an invincibility shield, yes, it wouldn't be an unsafe assumption to say that Sin destroyed the city under the Moonflow.
It would behoove you to remember that the technology after 1000 years would have taken a downgrade. Unlike the old Bevelle, the current city did not pour all of their effort into raising a mechanical army. Additionally, the capabilities of a Summon are tied in direct link to the Summoner; this also implies that if the Summoner dies, the Summon will dissipate. Why blast your way with mortars and shells into a meat tank made of pyreflies that can instantly be called again, when you can kill the source, instead?
Also, perhaps some clarification on the timeline would help. Bevelle and Zanarkand started some war together about who knows what. Bevelle was winning at the time; Bevelle was actually winning the whole time. This fact is implied in FFX and it is confirmed in FFX-2. Sin was summoned at the end of the war, after Zanarkand had been beaten into the ground. It's a little hard to restock on Summoners, but what you can do is restock on machine parts. Sin was summoned at the end of the war, after Zanarkand had already lost. It was a last ditch effort on Yu Yevon's part to have a moral victory, if not a physical one.