Gus

That's mostly normal. A twist converter can't fill completely in one go because you're pulling against an air bubble with nowhere to go, and 60-70% is behaving as designed.

To do better: fill, then with the nib still submerged twist the piston back down a quarter turn to expel some air, and fill again. Two or three cycles gets you nearly full.

If it stops at half and doesn't improve across cycles, check the seal. A converter not fully seated on the section nipple leaks air and never builds vacuum. Push it on firmly with a slight twist and you should feel a definite stop.

One drop of dish soap in the soak water. Not more than a drop, rinse thoroughly afterwards, but it lifts the film that plain water leaves behind.

Weight has almost nothing to do with fountain pen friendliness. It's about sizing and fibre. A heavily sized 68gsm paper takes ink beautifully and an unsized 120gsm sketch paper wicks like blotting paper. Thick and coated get marketed together and they are not the same thing.

What you can do with the notebook you own: use a finer, drier nib, since an EF steel puts down a fraction of what a medium does, and pick drier inks, because the well-behaved document inks and most iron galls feather far less than saturated dye-heavy ones. Writing slower helps more than you'd expect, since contact time is what lets it wick.

What you can't do is fix the paper. Nothing you apply to it helps enough to be worth the effort.

Second the paper point strongly. A 30 pound pen on good paper beats a 200 pound pen on whatever pad the office buys, every time.

Direction-dependent scratchiness on an otherwise fine nib is usually alignment or rotation rather than a defect.

Under the loupe, look at the tines from directly above with the nib pointing at you. They should meet with no step. A tine sitting even slightly higher than its neighbour catches only when you pull in the direction that digs it in, which matches what you describe.

Then check rotation. Most people write with the pen rolled slightly and have no idea. Deliberately roll it a few degrees each way while doing an upstroke and see whether there's a position where the drag disappears.

Steel nibs do smooth a little with use, but break-in is doing far less work than the internet suggests.

Then you choose: retrain the grip, or have the nib ground to how you actually hold it. Neither is wrong, plenty of people write beautifully at a rotated angle with a nib ground for it.