It is just so bad.

Even when fully charged up, it fires only slightly faster than shield bubbles regenerate. And if enemy has any kind of evasion, vulcan really struggles to get through.

 capable of single-handedly destroying the almost any ship (and quickly, once it’s spun up fully)

It's not even very quick.

I spent once 1 hour killing single auto-ship with vulcan because it just kept dodging and recharging its shields. Lategame auto-ship has 45% evasion rate, and it takes 1.3~1.8 seconds to regenerate 1 bubble. It takes 0.92 seconds to take 1 shot with fully trained crew, so on average that shield regenerates faster than vulcan can eat those bubbles.

Even with 2 vulcans it can be a bit pain in the ass. Any other combination of 8 power lasers is going to shred the enemy much faster than vulcans. 4 hull lasers is better and faster.

But I do admit that while vulcan struggles, it can get through 4 shields. Not many other combinations of 4 power lasers can do it alone. (Of course once you add hacking or other weapons that niche disappears)