It takes time to process each person through the TDC, and if they don't have Pre they slow down the process, especially when they argue with the TDC that they should be let through anyway.
So, I think the BP checkers are a necessary evil, and trying to bypass them as you describe just makes you a DYKWIA
I disagree. The bottleneck is at the security check point, not TDC.
The reason airlines hire the BP checker is to enforce elite lines. TSA doesn't care about your status. And TSA doesn't own the line, so they aren't going to send someone patrolling it. I personally know a few TSOs and they are not paid well at all for the hours they work. Retention is low and that's the problem. You get a bunch of clueless people with no motivation. The airline/airport hired guys are even worse. You get what you pay for.