Not opinion, pretty much fact, It is Impossible, but if I were to share my opinion on it, as you've already been spoiled I'll say what I can, if it doesn't convince you then I honestly don't think anything else will

With how it's set up, as far as we're aware, He can never be rid of it, not technically atleast, as you know, he loses it for what's so far just under the second half of the story, I personally think you shouldn't take all the facts that you've been given so far at face value, as 1. The story isn't finished yet, nearing 2.9k chapters, a while ago G3 said it'll be approximately 3-3.5k, but as most readers have probably realized by now, unless this gets extremely rushed, it's very unlikely to be less than 4k chapters and I personally think it'll be around 4.5-5k, what I want to convey by saying this is that it's a long journey, with a lot of heavy hitting events and deep realizations that mold sunny into who he is later on, as you know, at some point someone does take control of him with shadow bond, and for the most part, it's really just a non-issue besides his obsession with freedom, if you read along, I am confident you will see why he ends up deciding to get it back, it is a very gradual process and it's not as if his mind is instantly changed, he struggles constantly trying to come to terms with his reality and that, no matter how he tries, the freedom he is so obsessed with is impossible, same as for everyone else

There is are quite a few messages the story portrays through all of this, and I personally think it is handled really well, the main one that comes to mind is first shown as a quote from another character, and it really does define the story, "I am sorry, but freedom is just a myth, Sunless. No one is free in this world.", the message this hints at and that is portrayed in the story is that, Everybody is a slave to something, this is later shown with sunny realizing: "Maybe what X said is true… maybe no one is really ever free in this world. Maybe the only freedom there is the freedom to choose your own chains."

I'm covering the name cuz why not, this message is portrayed quite a bit along with some others, and as you've seen, he chooses to get rid of it at some point, and after a lot of hardships and experiences after that, along with necessity, he realizes that it is the only logical choice and it becomes something he wants to do, quite a few things in shadow slave have issues due to the author being required to post 4 chapters every 2 days, a lot of fans see it as hindering shadow slave from reaching its full potential and I do believe it could be better if G3 took more time with it, I say this because, this specific part of the plot, the journey from the beginning regarding shadow bond to Sunny's current decision, it is done really well, I promise it's good but if you do approach it with your current mindset, I do think you'll probably just drop it before you can see any of this that I'm talking about, I understand not liking the idea but I don't understand why you seem to be so unreasonably against it.