Quality of knock-off brands like Jinhao and Wing Sung is going to be pretty universally shit. You can usually buy a handful and one will be at least decent though.
That’s just not true. I have 35 Jinhao’s, and ~25 from other Chinese brands like Moonman/Majohn, Wing Sung, Hongdian, Lemon, Asvine, Kaigelu, & more. Out of all of them, only 2 have been duds; one was a Kaigelu which had a bad nib that I was later able to fix, and the other from a no-name gamble which was horribly unbalanced because they added brass to the finials to make it feel more substantial. The nib was pretty decent though, and it at least looked pretty. Everything else has been fine to excellent. Are they all going to be 5 stars? Of course not, but considering the majority of them were under £20, and around 75% of those were under £10, they’ve been great. Definitely no worse than Lamy, Kaweco, or any other western brand in that price point. The more expensive ones have all been fantastic.
Granted, there are still some that aren’t good and should be largely avoided. Generally, pens that you can’t find a brand name for will always be a gamble, as are the 4-digit model number Wing Sung’s. They’re a different company than the 3-digit ones and I’ve only ever heard bad experiences about them. But on the whole, Chinese pens have come a long way. Don’t be so quick to dismiss them completely.
On top of what others have said, it’s worth checking that the nib & feed are properly seated. I’ve had that happen with TWISBI’s before and that was the issue.