I don’t think that Rey being suddenly chosen by the Force is antithetical to canon, and in fact it goes back to how the Force might usually work in the galaxy according to the '77 film. Anyone can learn to use the Force, and anyone can be suddenly chosen by it to do great deeds, hence the ‘may the Force be with you’ benediction. In fact, it seems unusual for the Force to be passed down through bloodlines, with the Skywalker family being one of the few examples of this. For most people, most Jedi, the reason they have the Force is a mystery, even if it’s usually identified early in their lives. But remember, Midichlorians are only a symbiote with the Force, not the reason for it. A person could suddenly be chosen by the Force later in life and then accumulate Midichlorians that communicate with it. And Midichlorians aside, the Force choosing a person for greatness is a very Aurthurian legend way of the Force working, with Rey being called to the Skywalker’s sword.
Maz tells Rey that the Force has ‘always been there’, but Maz isn’t a Jedi, she’s just very old. There’s no indication that she has the desire or aptitude to be a Jedi, so I think it’s a fair expectation that Maz is just telling Rey that the Force is available to everyone in some capacity, at all times. She could just as easily tell this to Chewie and it would be true. When Rey later says that ‘something inside me has always been there…now it’s awake’, she could just be referring back to Maz’s statement about the Force and not that Rey was always special. In fact, the important part is that awakening, the Force choosing Rey to accomplish some destiny.
I think that’s the point of TLJ, in my opinion. Rey comes from nothing, no special creation or lineage, and it’s only a chance awakening in TFA that brings her into the story. I don’t think that Broom Boy was intended to have some special parentage, he just chose the Force or the Force chose him at the end of the film, just as it can choose anyone no matter how small. In fact, TROS itself continues this thesis when Finn discovers that the Force has awakened in him as well. No special parents with him either, and that’s what makes Rey’s special status so detrimental to all of this.
TROS’s revelation about Rey destroys TLJ’s thesis by saying that Rey always had powerful blood. Neither my Clone Rey idea or JJ’s virgin birth Palpatine creation idea is able to negate the destruction of TLJ’s thesis because both ideas state that Rey was singularly important from the moment of her conception, and always would be. The only way I can see to preserve TLJ is by establishing that Rey’s first moment of importance is her awakening in TFA, and the only way to do that while also talking about her past is if Palpatine foresaw this awakening and sowed the seeds of darkness in Rey before that happened.
And yes, in a perfect world Rey’s parents wouldn’t matter, but if we delete the flashbacks and that motivation for destroying Palpatine, well, that would just further diminish Rey’s motivation. We have to consider the practical impact of deleting more of this already eviscerated film.
I think the issue with Rey’s parents being good is less about their goodness and more about the way they are handled in TROS. It doesn’t make sense for her parents to sell her to Plutt to keep her safe, since no good parent would willingly do that. They almost surely could have chosen a better person than Plutt to keep her safe, so it just doesn’t fly that they would really have Rey’s wellbeing in mind.
However, there’s actually an issue with TLJ’s version of Rey’s past that ties in here. If Rey’s parents were trash who sold her the first chance they got, then they wouldn’t have sold her when she was six. They would have sold her as a newborn, as most people who aren’t able to raise a child would do. Even if they kept her until she was six, she probably would have been malnourished and sickly, not like she looked in the flashback. So this is a problem with TLJ, and this is actually evidence that her parents did care for her, at least a little. That is why I think there’s value in keeping the flashbacks, but just making it so that her parents were forced to give up their child. It is the best fit for the facts at hand.