I believe Jaska never was the problem in COB. He's super competent and has a style that fits perfectly Alexi's (a bit like Ulrich's drumming fits perfectly Hetfield's songs despite his lack of technique). I believe the real problem in the band was Janne. It's been years that he seemed like he didn't give two shit about the band. He said he didn't like their earlier works, then he hated the whole neo-classical aspect of the music because of how difficult it was to pull-off and he basically said he enjoyed just sitting back and playing some background chords. He just became lazy and I'm pretty sure that this was a drag for all the other members. I too have high hopes for what's coming next. However, it won't really be CoB anymore, but it might still be great !