Which size nib are you using? If it is Extra Fine (EF) or Fine (F), then it can be scratchy. Moreover, Japanese EF and F are generally smaller than other EF and F.

I have a Lamy Safari F, which is super smooth and glides. My Pilot Metropolitan also has F, but not only is it thinner/smaller but it is not as smooth. I won't call it scratchy but it could be construed as such.

Also, paper matters. Fountain pens generally prefer a smoother paper, especially one that doesn't absorb much ink.

You will also need to see how you are holding the pen and the angle the nib strikes the paper. You may want to search online for some advises on that since that can make a world of difference.

Edit: Almost forgot, the more you write the better a fountain pen gets since the nib adjusts to your writing habit. I had an old Waterman when I was in high-school, which I don't have anymore, and so far no pen has come close to it in smoothness.