But I've seen some speculation that after all the awfulness of the confirmation hearings accusing him of being a hard-right leaning justice that he would actually try (consciously or not) to show he's not locked into that mindset.
That certainly could be true. I like to believe supreme court justices remember that with that role comes with the truest ability to be impartial and unbeholden.
The justices probably don't believe that they are partisan. Rather, they believe that their own perspectives represent objective truth.
The same things (and worse, IIRC) were said of Roberts, and while I disagree with some of the rulings he has made, he's been remarkably unpartisan.
I believe all of these justices care a lot more about their legacy of justice and the sanctity of the court than anything else.