Yup, good build. 900 range weaponry, a crucial large ballistic for HE, and harpoons just kill things. What build are you using in terms of hullmods/flux stats/etc? I find it difficult to maximize the potential of both guns and missiles on manticores (which is by design, without the tight OP their weapons package would be even better).
IMO the manitocre pays for it in terms of low speed + poor shield + inconsistent PD = quite vulnerable to getting swarmed and missile strikes against it. And its damage balance is a bit low on kinetic for endgame fights. But if it has some ships around to help it not get focused and to provide shield pressure (like a squall boat) then those are mitigated and the strong points shine.
In terms of "the best" for destroyer endgame, I'd say it is up there, depending on wanted role. Sunders give significantly better direct damage (HIL and sys-ex high energy focus) at longer range (1000*range modifiers + 200 vs 900*(range modifiers + 10% ballistic mastery)), with higher speed, at the cost of missiles. Medusas have much less damage and also no missiles, but is so tough and mobile that in role it is a hyper-mobile monitor with ok guns.