[cabraca]

ok lets break this down: you say that guy is "very gregarious and extroverted — the business folks like him" und your manager "is somewhat of an idiot".

could it be that your tech lead is stepping up to fix the mistakes of your manager? sounds to me like that guy might be the buffer of the team. the person that catches the shit the business folks fling at the team to allow the rest of the team to get some work done. Of course this impacts his "real" position as a tech lead.

its natural that the second in command (sounds like thats you) steps up to fill the resulting void and take over tasks. maybe you should talk to your techlead. ask (not accuse) him whats up with your observations. communication is key in those situations.