I don't think HxH is popular solely because it's long. I think that HxH is great, but its' strong point is being able to be great over a long period of time, providing more entertainment, while most masterpieces are short and compact.
If we're talking about a great world, foreshadowing and rate anime in terms of worldbuilding, then yes, HxH is up there with giants like One Piece and Naruto. However, HxH isn't fully finished, and that's the problem, storylines have not been concluded which gives a pretty shitty feel to it. It probably will never be finished either.
HxH is higher quality than One Piece and Naruto overall though, but I prefer the worldbuilding Naruto and One Piece have, more well thought out, might just be because they're further in, resulting in more fleshed out storylines.