Regarding Raine's vocals on HIPT, I think Bob Rock's influence on the vocals was as much to do with his recording and production of the album material itself as the change in style. Yes Raine's voice and style were changing, but Rock was also trying to develop a fuller sound for the band, like he had previously with Metallica, but OLP just isn't that band. So I think that really affected how the vocals turned out here, and to a lesser extent on Gravity.
I think Arnold Lanni was the opposite, playing to the band's strengths, which is why we all fell in love with them. So that's part of why it was so poorly received. It has to be recalled that at the time, many of us were apprehensive after Gravity about what kind of band OLP was going to be, and then when HIPT was underwhelming a lot of fans left.
As for the album itself, it might have been more well received if the final product was closer to what we heard on the demos (they killed my WTSOYF so bad). I think that was also Rock's influence, as the edge and tension of the demos got replaced with something much more straightforward and, to many OLP fans, uninteresting. I admire what Rock was trying to do sonically to break OLP as a mainstream act, but again it didn't play to their strengths.
Additionally, I think the behind the scenes videos didn't help much, seeing how much tension and frustration and confusion they were going through as they were making HIPT. It could really be heard on the album.
All that said, I still listen to HIPT fairly frequently, with Picture and Love and Trust are playlist regulars. It's certainly grown on me over the years!