You say negative impact, but most of Oda's target audience (Teenage Boys) might not find it so. Much of popularity of Shonen manga is build up on people being tired of more cynical and dark motives, and just wanting to read something pleasant.
You say negative impact and some would say happy ending. We are currently operating under assumption that there is some future story purpoes for Pink. If there is not, Oda might decide that his son being alive and his wife waking up is a proper end to Pink's storyline in One Piece.
I got that award for being fucking insane, to be honest. Arguing and disputing with up to fifteen people at the same time? It got to the point where my posts constituted almost half of your average chapter thread.
I disagree attack on Titan sees death all over the place and popularity wise has no problems what so ever.
So death or no death isnt such a big issue here. Not to mention how Game of Thrones (tv series name) novels are seen and exactly why they have such appeal and here is where I am getting to my point.
Oda does not wish to kill his characters because he believes crushing someones dream is a lot worse then just killing them. Ok I get it. But the absence of death (i am not saying 100% but to the point that is evident that it just wont come to the main characters) is what takes away from investment into the fighting scenes. You are never really worrying about the strawhats, like in worst case they ll get beaten but will at some point in the future return the favour. While on the other hand, knowing that someone can get badly injured and taken off the story at any moment creates the real suspense, prevents people to see the pattern and makes it exciting.
Thats the gist of Song and Ice and Fire success imo, that there really is no guarantee that X will survive or that all will go well so you watch not just to see how the hero will win, but IF the hero will win.
Which in the end creates a better experiences for the majority of people.
Now no way am I saying Oda should start killing people off right and left or SHs for that matter, but "shock" therapy like people actually dying from guns straigth to the face etc, bring a lot more emotions into the overal story than if we all know Law will be fine and are just waiting to see how he ll get fixed and in what way.
Dont get me wrong. Oda has his formula, its working for him and he wont step away from it, but I personally would have loved to see that. The real presence of danger. And this is why for me Marine Fort, although I was quite sure WB may die was a bit of a shocker and in a way nice, when Ace was taken away as well. Since it was like, holly shit didnt expect that and it created a more tangible anti-feelings (or love feelings for those who hated Ace) towards Akainu, aka in this guy means serious business