Aww. I'm sorry you've found it disappointing.I've heard about some of the older bottles of Lamy Blue-Black being iron-gall so perhaps that would explain why it didn't seem washed out to me.
I really like the Pilot blue-black cartridges! But I'm also partial to Pilot pens. I bought a couple of Kakunos when I was in Japan two weeks ago, and I absolutely love the blue black cartridges! I haven't tried the blue black Lamy cartridges, but I feel like the black cartridges get a little washed out too.