It would be nice if it had a little more health. Ideally 800 health, at minimum 600.

Vanilla Autocannon takes 350 steel and 40 plasteel and has 380 HP.
A steel Vulcan Cannon on the other hand takes 800 steel and 100 plasteel and has 500 HP.

It takes over double the resources and in the best scenario 12,000 research points if you have a tech advancing mod and you're on Spacer tech or 14,000 if not, this amounts to over 10x the research if you count from Gun Turrets. (Autocannon you can research immediately after Gun Turrets for 1200 points while Vulcan needs at least 12,000)

So yeah, a lot more resources and research for only a 31% HP increase. That being said the fact that the Vulcan doesn't have cooldown already makes it immensely powerful despite the low armor pen, I just wish it had more HP for the resources.