I'm not sure if either of you are right, at least with regards to chasing just one item; the big hidden variable is what the odds are for an Item Type matched against the Quest Points. I've been getting Hooks at every level of fish, including some at near the total cap, but they're almost always Lava Hooks at huge fish points. What I don't know is whether you get less hooks at high than you would at low fish points, which would answer whether dropping a quest matters; If you get more Hooks at low, or just more likely a wider range of Hooks, dropping would make sense as even a 6 liner isn't going to be too high with the fish being kept at size 10. If it doesn't matter or it makes it more likely you'll get a Hook (even if it turns out to always be Lava) at higher points, not abandoning quests to keep the average quest high would be useful instead... not assuming a corresponding increase in how much fishing has to be done to fill them of course!
What I can say is, if you're not after Bait, you're in the wrong business

67% of the total of every result seems to be remaining consistent so far!