Maybe "authentic" isn't the best word to use in this discussion, but I'd ask, echoing Finn, if the live show is the measuring stick by which we deem the worthiness of musicians.
I love these guys. As off-beat as it is to do mariachi renditions of hard rock songs, their arrangements are pretty flawless in my book. And, their shows are probably the best live performances I've seen and the crowd has such great energy. The crowd in this video is probably on the tame side of things for one of their shows. I also have their studio albums. To be honest, they're not great. I mean, they sound good technically and they play well, but without the collective effervescence of the crowd's energy playing off the band's energy, it's just ok. I can't go to one of their shows and not bachata, but I could listen to one of their albums while doing dishes and it would just be background sound.
Conversely, you have the Smashing Pumpkins. That was the band that got me through high school. I think their studio albums are pretty amazing. But, live? Let's just say Billy Corgan's singing is a little rough, for starters. Even with a production team, a show can be really hit or miss and probably more miss.
Now, what's authentic? You can poke holes in Metalachi as some of the folks in the band who "act spanish" aren't actually Latino. However, the performance is putting your money where your mouth is and they deliver. On the other hand, Billy Corgan is a fantastic composer, just not the greatest performer. Is he any less of an artist for it? Probably not. But, as I've been typing this, I've been listening to Here I Go Again/Bidi Bidi Bom Bom in the video above on repeat and wishing I was at a Metalachi show.
BUT, and this is a big "but", I'm also not the kind of person who's all over Reddit and instagram and whatever going on about how second wave Smashing Pumpkins is a "flop". I do my own thing and everyone else can do their. I also think there's a big dfference between saying that the live show matters to me (and I might value a band more by that criteria) and that if a band can't do a live show, they should pack it in. And, I think that's a big thing. There's so much second rate trash on the internet made by people who (perhaps ironically) have nothing authentic to offer themselves, so instead they latch on to something else and find a way to sensationalize something about it for likes. Those who can't do,
teach instagram.
