Right, but it's had tons of other spinoffs, on more popular platforms, that haven't had near the success that some are expecting.
So why would this be so special?
Looking at stuff that One Piece is succeeding in, such as licensed media in general, where Dragon Quest has limited presence outside of the big game launches, it's hard to see that.
During the time following Dragon Quest III, it was easy to see, with stuff like Dai's Adventure really taking off, but nowadays, everything seems limited to just games.
so all the merchandise, local, cafè, food, accessories, app...don't count? if there is something extremely popular in Japan it's DQ
EDIT: btw, why is setting the bar too high looking at it thinking that it could be able to surpass One Piece, if we already saw this:
[PS3] One Piece Pirate Warriors - 85+26pt
[PS3] Dragon Quest Heroes - 115pt
[PS4] Dragon Quest Heroes - 70pt
One Piece = 111
DQH = 185
Not counting the already sold copipes of DQH (the ones included in the PS4 bundles: does someone remember the number?)