Eh, I personally do think that's pretty over simplified. But then again, while there's a few tracks throughout Opeth's career that I may not like all that much, they're a rare band I can say I pretty much love all their material. I really think each album has it's own specific flavor. Of course, there are certain 'eras' of similarities or even purposeful relation between albums, but each album has it's own statement and I think Opeth has had a pretty varied statement for the very specific genre they stuck to for so long. I love it though, the slight change through their career and then out of nowhere, Heritage.
Anyway, as I said, of course Heritage and PC have a similar vibe, but I think that's where it ends. I wouldn't go nearly as far to say that they're 'essentially the same'. Then again...we've got different ear holes! It's interesting, for sure. We simply hear it differently. To me Heritage was all about restraint and whispering ambiance, along with being pretty dark and foreboding; PC feels very much a 'bright' evolution of it, but it's so much more vibrant, varied and has many more ups and downs to me. It's still dark in places, but I feel that tonally, it's a far cry from Heritage's somber, restrained approach; PC feels louder, more versatility and eeriness. I've seen a few people call it boring and I simply don't identify with that at all; I can't see it. Which is fine, but yeah it's strange how utterly different people's view on the same songs can be.
That's part of the fun though.