Give me your fishing results!!
Because that is the Great White Whale of a question, and as yet, no one has landed the beastie for sure!
But, outside of the Devs, the data we have above is the best guess we can make. As the submitter of the largest share of it, let me explain using scrolls as an example what I believe happens. There are two rolls. One for item type, one for item intensity. Bait seems consistently to be the most likely reward, running at 67% now constantly for the last 200 submitted results. I believe then that the Item Type roll is fixed, irrespective of fishing quest level.
In the case of Scrolls, which I suspect is one of the available item types, I checked through the document for the highest level a 110 Power Scroll dropped at; 120 points coincidentally, the same as your 115 and 120. To give you some more figures, out of 634 results so far, 120 points has appeared 26 times, or 4.1% to give you an idea of the relative rarity of that level of fish quest. (these figures are not exact in practice, as the submitters are at differing levels of success and skill, and it's distorted by the way they hand in quests). If you look at those 26 results, you'll also see a 120 Power Scroll appear for us at 120 too. And also a Lava Lobster Trap.
Thus I am pretty confident is saying that, apart from Bait which does seem to always give Legendary Fish Bait at higher levels, even if it won't give you some artificially rare ones, the second roll for everything else can also include a very low level reward. I just completed a 140 point quest, very near my highest quests so far of 150 too... and got a Lava Lobster Trap again. This is because I suspect I rolled Item Type > Gear, followed by a low roll for Intensity and thus got Trap. Or maybe Trap is considered a high reward, compared to Hooks?
You asked about the Oracle Of The Seas; I believe that's likely the "Top Prize" for Gear. The document only has 1 successful roll for that. It's mine again, I've been using it to host Charybdis for people on Europa. 1 in 634 tries so far, although I've done hundreds more before starting to record them in public, also without success. I can also state, at least as far as the records go, I only ever got the Charybdis Bait myself once too, and once more for someone else, so 2/634 so far for that; For a 120 PS, it's 4/634 and for Void Lobster Bait it's 1/634 again (also me again). Thus what ever the "Top Prize" reward is for each loot table, it's got extremely poor odds.
The reason for this incredibly low level of reward is I believe because having to beat both rolls means the odds are multiplied and thus become as vanishingly small for the prize people want. Let's say it is indeed somewhere near, as the collected results show so far, 67.3% Chance for Bait, 18.12% for Fishing Gear, 7.6% for a Book, and 6.92% for a Scroll (assuming I'm right in dividing them into those types)... you have to beat the near 7.5/10 chance of Bait or Book before getting a shot at the Oracle or 120 Scroll, and even if you do you then have to beat the odds on a second roll to not get a lower reward and thus waste the opportunity.
And then you have to roll the quest having high points itself when trying again to influence that second roll... oh dear.
Of course, I may be entirely wrong; however the recorded sample so far seem to indicate that, for
some reason you definitely do get both a variable reward at a chosen point level, and hardly ever get the good stuff out of the system.
