Oh yeah I think he is a proper band member (after all he's credited along with the others on Uno Dos and Tre), I just don't think that means he has to play the exact same role in the band as the others. I think they didn't make a big announcement like "hey everyone meet the new official member of Green Day!" and instead just let his rise from being a touring guitarist to playing on albums along with Billie Mike and Tre speak for itself for a reason, seems like they want it to be a thing where he isn't obligated to play as big a role as the others if he doesn't want to. I'm a massive Jason fan and all for him being right at the front and in the spotlight more (I really enjoy being on his side of the stage at shows, watching him play and waving at him while most people are looking elsewhere is fun ), but I think he's just naturally more understated as a performer so it's to be expected that he's not.