@MarkRain
Indeed, blast core was introduced as Wakatsuki's "fang" and I was just noting that he didn't use it in this fight. Which is not surprising because it's a great technique if your aim is to destroy a sand bag, but it's not good for much else if your opponent is aware of it and it simply couldn't be mixed in the flurry of punches and kicks he was throwing at Ohma in order to keep the pressure up.
I would not say myself that the blast core is very bad against demonsbane. We've seen Ohma fail at the demonsbane because he's not that good at making his body go limp. Similarly, just as there are limits to what Ohma can take with indestructible, there are limits to what Ohma can redirect. So honestly, I don't think we can tell if demonsbane could successfully counter blast core and end catastrophically for Wakatsuki or if it would end up catastrophically for Ohma if he's unable to counter it. It's also possible that even if he could counter it, he'd still get damaged because the technique is so strong. So in my opinion, it's something that could go either way depending on their condition and how much they polish their techniques; I wouldn't claim that either technique is better than the other when matched against each other (although demonsbane is clearly more useful in a fight, it's also not exactly one technique but more a collection of techniques relying on the same principles).