I have a Pilot Metropolitan fountain pen. It's a nice pen but I don't use it for a few reasons. First, the ink evaporates very quickly. Secondly, the ink is always uniformly dark. I like that I can vary the heaviness of lines by varying the force I use as I write. Third, they are messier.
Interesting: I own the same pen, but do not have the issues you listed. Mine is a Medium, but light inks remain light (i.e. the flow is not thick).
If you meant that you want the thickness of the ink to vary with angle, then yes - most modern fountain pens are designed that way. However, they do also make the "italic" type ones.
With ball points, I can vary the heaviness of lines by altering how hard I press the tip into the paper. Very light pressure yields very faint lines. A fountain pen is uniformly dark, which I suppose what most people want for writing.
I have the same pen. I prefer dark and rich lines, as long as it dries immediately and does not bleed.
One thing i do with all fountain pens are to resurface the nibs using dremel or grinding on any fine surface. Basically a hit and trial to get fine calligraphy like quality, writing after that is more consistent and in control.
