It’s so bizarre to read this in the present, knowing how incredible TNG was, but I get it - the original crew WAS Star Trek to them.
The dedicated fans revived this series in syndication, well after it had gone off the air in 1969, and felt attached to the characters that they had obsessed over between then and the 1980s. Like modern fans, they thought that departure from what they knew would ruin it.
I wish I could go back in time and tell them that TNG is going to rock.
As a TOS fan who wasn’t too happy with what I had heard before TNG came out, I would bet against you. Most of them probably became TNG fans eventually, because the most impactful thing a show can do is simply to be great. Canon complaints and complaints about characters not returning are mostly about nostalgia, and if the show is compelling (especially if it’s compelling in a similar way to the old show), nostalgia can’t compete. If anything I’d guess that the people in this article were more likely to become fans of TNG, because it would have exceeded their expectations, which can make things seem better than they would otherwise.