For what it's worth the game has been doing quite well on Amazon US, being right behind Link's Awakening at the #5 spot for about a week now.
I think it'll at least do better than it did on PS4. Though, I honestly don't care if Dragon Quest becomes huge in the west. I just want it to sell enough for the games to keep getting localized. So, I think the series will be fine from here on out. The game has a great metascore, great reviews, tons of content, Japanese VO, voice acting... Hero is in Smash...I don't know what else Square could do to make the west care about DQ as much as Japan does.
People say Dragon Quest is too traditional, but there are games that are as traditional as Dragon Quest in terms of gameplay that do just fine (Pokemon, Persona is turn based, non action, etc.) Bottom line for me is, no it's not Final Fantasy in terms of sales, but it's far from the bottom of the JRPG totem pole in the west. You have series like Legend of Heroes, Ys, Shin Megami Tensei, Tales, Mana, that don't perform all that well in the west but still have active fanbases fueled behind regular localizations. That's all I really can expect from more niche JRPGs. And to be honest, I'm fine with that.