I am just attempting to practice copperplate on all purpose paper. I have a G nib already, the Takinawa and it is really scratchy on the paper and very stiff. I would think that a more flexible nib would be better not a stiff one as is suggested.
Flexibility and smoothness are not necessarily connected, but
@neriah is correct that often more flexible nibs can have a finer point, and thus be more liable to be "scratchy."
Any reasonably smooth, commercial paper can work in terms of scratchiness. I would stay away from anything textured, like the "linen finish" papers, or some 100% cotton papers, and hand-made papers are right out.
Most of the time a scratchy nib is either misaligned tines, one tine is "higher" than the other when seen through a magnifying glass, or technique. Developing the very light touch it requires to write with dip pens can take some practice. A steel dip pen will never feel like a ball point, or roller ball or even a fountain pen. They will always have more "feedback", i.e. you will feel the paper much more under the pen. If you are regularly catching the nib on the upstrokes, then a lighter touch is needed.
If your tines are mis-aligned, then you can either try and push the high tine down to meet the lower one, or get a new nib. Sometimes just flexing it carefully on your thumbnail can put them back into alignment. What you don't want to do is push the low time up to meet the high tine and then end up with a slit that is too wide.
You can also have a corroded tip, and that will make a pen feel scratchy. If a new nib feels better with the same ink, paper and nib, then it was the old nib and it should be discarded. If the nib has always felt scratchy, then check for alignment. If it's aligned, you can try and smooth the nib on a very fine hone, or even one of those three-grit fancy nail files found at beauty supply stores. There are two rougher grits on one side and a buffing grit on the back. Fountain pen folks use those for polishing the hard iridium tips on fountain pen nibs, so they'll work a treat on steel.
Or just get a new nib.
Andrew