Pirate metal is probably seen as "ironic," or maybe just too niche to deserve a top level genre (how many bands besides Alestorm are there?). Viking metal has a long history, though, given the Nordic roots of many extreme metal genres.

That being said, I don't think Viking Metal is too helpful of a genre anyway given the completely different sound of, say, Ensiferum vs Borknagar, or Tyr vs Windir.

Running Wild was the first to make pirate themed power / speed metal

Everyone's mentioning Alestorm - where's the love for Visions of Atlantis? It's not even ironically good, it's just good.

I would argue that the existence of Bathory alone is good reason for having a separate Viking Metal category.

They do? I see Folk/Pagan/Viking as one genre when I browse by genre. Alsetorm (sorry, don't know of any other pirate themed bands) has some folk elements so I think it fits.

I've never heard of this sub-genre. I assume that's not like Savatage's Wake of Magellan.

Argh? You mean Arrrrr! Alestorm!!!

Alestorm, the world's second best true Scottish pirate metal band!