Never said it was as expensive as the Vigilant, just expensive for the performance you're getting.
That said, in the currently pvp landscape, I don't think the Ashimuu is a good ship.
Sure, it may cap out a Vigilant in 35 seconds, but how many of those do you see?
In fact, outside of FW, how many people can honestly say that they come across comparatively high numbers of cap-using ships?
I know I don't. EVE is a Drake+Minmatar game. All that neuting is going to do is let you run away once they drop point.