I'm personally leaning marginally to keeping accepted answers pinned to the top. I've personally experienced some great benefits from being able to 'pin' answers to the top. That doesn't mean I don't realize there are downsides, but I think keeping answers pinned outweighs those.
Unpinning accepted answers on Stack Overflow is part of a project focusing on outdated answers. I think for this site, outdated answers aren't really a big problem (yet?). Yes, this site has plenty of questions/answers that were written before the citation expectations were put into place, but unpinning an accepted answer there isn't going to magically make better, backed up content float to the top. It's been agreed upon to not delete all those answers either, so I don't think unpinning answers is going to help anything there.
Accepting an answer is supposed to mean 'this worked for me'. I think answers that truly worked for someone else could deserve a bit of extra highlighting. Especially if they're not the crowd favorite. One problem with a site as subjective as IPS is that the votes from others, especially HNQ, can skew things a lot. This site has had plenty of struggles with answer quality, because users ignore cultural context, because users are distracted and start giving their opinion on tangential details... And then the votes start pouring in, and they're all 'agreeing', especially if there is a 'popular opinion' or the answer just fits their own cultural biases better. I think it's good to give askers just that tiny bit of control over their own posts, give them the ability to say 'but this was truly helpful to me', because seeing the votes so skewed to something that isn't even helpful to you creates a very 'helpless' feeling.
I've personally experienced most of that when this question of mine reached HNQ. It did so with an answer that totally disregarded the part where what I was asking for was a normal thing to do in a Dutch context. That answer is now deleted for not answering the question and disregarding the cultural context, but it still has a higher score than the accepted answer at this point. Even while it totally wasn't helpful to me. I was glad I could override that by accepting something that was helpful while the answer was still up and outscoring other answers. While at the time I hadn't had a chance to put the answer to practice, it did make me realize what I had done wrong and how I could do better next time, which made it infinitely more helpful than the one everyone on HNQ seemed to 'like'.
Sure, sometimes a bad answer gets accepted. And yes, that's very annoying, but that's mostly because accepting an answer impedes clean-ups: Accepted answers can't go in the low quality answers queue (they will be removed from it if they're already in it) and it will block the Roomba from cleaning up a closed question in 9 days. But, those can be fixed: Moderators can still clean up those answers if they don't meet the citation expectations, we can manually clean up the questions that can't be Roomba'd, and with the ability to also remove questions from HNQ, we can avoid showing questions with 'bad answers' to the entire network.
All in all, I think for this site, the positives of being able to pin an accepted answer to the top of the list outweighs the downsides. To me, the ability to say 'this was most helpful to me' and to overrule the crowd favorite, to overrule voting that's possibly biased by cultural differences or popular opinions seem more important for a good quality site than always having the top scoring answer at the top.