As far as Western exposure to Japanese acts goes, 99.9% of it comes from three arenas: anime, dramas, and novelty.
B'z have only really provided theme songs to one anime (the subject of this forum, conveniently) and it's not one of those that really broke out in the US/Canada (with better success in Europe but still nothing compared to the other major series that were more easily digestible). At best, exactly as you said, they will seem like "just" a Japanese rock band without a "visual" hook to make people care about it any more than they would Aerosmith or any Western rock act. Couple that with the fact that most of the songs are in Japanese and you'll have trouble getting most of the non-anime persuasion to even listen ("can't listen to nothin i dont understand [unless there's a girl dancin around]"; there are some strange fans of certain acts out there...).
It's also not a coincidence that (possibly aside from "ultra soul" being covered on endless karaoke programs and "Into Free -Dangan-" from the video game Dragon's Dogma) the best-known B'z song in the West is "Ichibu to Zenbu"—their only major drama theme song of the modern era, for the 2009 series Buzzer Beat. The drama was a huge success due to the star power of Tomohisa Yamashita with that audience, so the song became a "hit" with overseas drama watchers. One thing that's for certain is that there's an obvious consanguinity between "anime/drama fans" & "hardcore J-pop fans", but B'z don't really source their support from either of those communities, so that alone will reduce the amount of people that would naturally ever even hear of them without speaking with natives about non-anime music. Another problem will be that B'z falls under the hard rock & guitar music genres. Most in the anime communities lean much more toward pop music with minimal rock elements, which (especially by modern conventions) really isn't very compatible with what B'z releases. In terms of homeland success versus relative obscurity elsewhere, look no further than fellow rock band Mr. Children. There will even be people reading this that have no idea that such a band exists and those that do probably can't name more than one song (if that many). Yet in Japan, they, like B'z, are a household name with a long history of success.
All in all, outside of anime, unless there is some visual element to the novelty of the act like Babymetal or AKB48, it's really going to be tough for any groups to break out overseas. If not anime themes, the only other surefire way to get attention in the West is to skew as far from "rock music" as possible and head toward metal and be known as a visual kei band (Dir en grey, X Japan come to mind). There are some outside of the anime world that will try those bands more openly due to various reasons but B'z still doesn't fit that mold at all.
Aaaaaaaaaaall of that is without acknowledging that B'z are ancient by "pop" standards now (Tak is 57, Koshi is 53), so in terms of people who are jumping onto the idol train after whetting their appetite with anime, they're more likely to skew toward the 16-21 year old talent farm output than a rock band that's been around since before many of the prospective listeners were born. Unlike most "music idols" in Japan, B'z have never appeared on a variety show and apart from occasionally appearing for an interview every four or five years, they essentially only record music and tour. Neither member even has social media, so in this era of idol worship, it'll be a bit hard if you're interested in anything other than the musical output—especially if you're foreign.
In short, it's hard when B'z...
☒ Doesn't do non-guitar music
☒ Doesn't do non-Conan anime theme songs
☒ Doesn't do drama theme songs often
☒ Doesn't do metal music
☒ Doesn't do visual kei
☒ Doesn't use young girls to showcase the music
☒ Doesn't do the variety show circuit
☒ Doesn't give interviews
☒ Doesn't do non-music photo spreads
☒ Doesn't have the ability to start now to be young enough for those interested in idols
☒ Doesn't produce a large amount of English songs
☒ Doesn't do social media directly in any form
All of that makes it difficult even for those already engaged with Japanese culture to even get interested, much less invested beyond that (on top of the fact that not every band is for everyone, of course). Take all of that away and you're trying to get folks to listen to something in a language they don't understand—an even more daunting task, especially when coupling it with rock music. Plenty of musicians such as those you mentioned have been supportive, naturally. On a related note, American drumming legend Carmine Appice name-dropped B'z in an interview a few years ago:
“Japan has their own domestic artists that are huge. It used to be that Japan didn’t have any domestic artists until the mid 90’s. All of a sudden they started getting their own artists. So all the American and UK artists who used to go there and play the Budokan are now playing smaller venues. But their artists are playing stadiums. There’s a group over there called B’z and they can play three stadium nights in every major city in Japan. We’re talking 150,000 people. It’s a singer and a guitar player. I went to see them in Japan as a guest, they’re friends of mine, and I think it was the night before or night after I saw Kiss over there. Kiss was playing at the stadium too. The B’z production was bigger than the Kiss production. It was ridiculous…it was so big. Over there they don’t travel around in big semis, they travel around in these sixteen to twenty foot trucks … so they must have had about a hundred trucks going from city to city … it was crazy. But there just huge over there.”
I'd actually be curious to hear how those that check in here first heard of B'z. I know for many of us it was through some sort of connection to the Detective Conan anime. I first heard "girigiri chop" and was shocked how different it was to all of the other included theme songs to that point. By the time I heard "ONE" in the third movie in the franchise, I knew there was something special in a band that could produce songs of such radically differing archetypes. A few months later, "Shoudou", "Yuruginai Mono Hitotsu", and MONSTER hit and the totality of the work was so overwhelming in quality that I've followed 'em since then. I soon therafter saw MONSTER'S GARAGE on DVD and couldn't believe what I'd been missing all those years; while I appreciated the limited studio output I'd heard to that point, it was seeing the live presence that sealed it for me. I've met a lot of great friends entirely based on the music B'z has made, so for that alone, I'll always consider it time well spent. Even beyond that, I decided to finally learn guitar after seeing Tak's stage presence (something I had long wanted to do but never found the right inspiration until then). Those I've met based on that hobby alone and those I've gotten to know better because of it are all reasons I'm really glad I discovered B'z when I did (I've also gotten to, gratefully, pass on that interest in playing guitar to others in the years since and encourage them to give it a try).
