I honestly don't understand this thought process. It seems like your argument is that to increase your QOL doing a particular activity in OSRS, the reward/item/boost to increase that QOL should come from the same activity and nothing else. So, you would want these rewards to only come from the fishing skill itself, correct? Except, that's just... not how the game works? Look at questing, if you want to unlock new zones, items (sometimes BIS), and even entire skills, there are quests you need to do. Sometimes, those quests have requirements on top of actually doing the quest itself. Now, it sounds like you consider yourself a skiller and someone who does not like doing PVM. What if I was someone who just didn't like quests, but really wanted to unlock the herblore skill? Well, too bad for me, I gotta do Druidic Ritual. Same argument to be made for countless things in this game. I want to PVM, I need Void armor, but to get it I have to do Pest Control, a minigame which is not PVM. I want an imbued god cape to make my spells hit more, but to do it I need to venture into the wilderness, a PVP zone. And do I even need to mention achievement diaries?
Your nightmare scenario of spending "hours" on the boss beforehand to get these cool rewards really doesn't sound that bad. I can understand that if you are completely against doing the content, then it's not about the time, since you are just opposed to doing it at all. But, in that scenario, it's the age old argument that you are limiting your account by your own choice. Jagex puts the content into the game, and in classic MMO fashion, the content has to have good rewards to make it worth it. If you still don't want to do the content, then the rewards must not be as great as you claim.
They are adding fishing content into the game (if the poll passes), but nothing is stopping you from continuing to enjoy the fishing skill as if they did not add it at all. So other players will be more "efficient" while afk fishing, so what? You are free to be just as efficient if you did the boss. If you choose not to, then it will take you a few more hours to get 99 fishing. I'll write it again, so what?