The conviction rate stuff is misleading. Some smaller offices that don't try many cases simply owing to lack of population and crime don't like to try them when they arise because they aren't experienced. They're afraid because they don't really know what they're doing. They're not trial attorneys. The get paid dick to sit around and plead out small potatos stuff. They like nothing more than to plead things down to dispose of cases. It's not about a winning percentage. It's a lack of competence and work ethic. They didn't take that job to try cases in front of juries. They took it to sit on their asses the vast majority of the time.
I've personally never once heard a prosecutor reference their conviction rate, though I'm sure there are plenty of fuckfaces out there that do. Idiots care about stupid things. It's also pointless, because if you duck cases that's the first thing your opponent is going to eff you in the press about over and over come election time. It doesn't save you. Letting crimes go uncharged is arguably far more publicly damaging than losing at trial. The public is often as or more upset with the jury. It's a hell of a lot easier to deflect blame at the end of a trial than it is if something goes uncharged. There's really no PR incentive not to take a solid case to trial generally speaking.
I don't think Meggs declined because he was worried about losing. If people thought he was guilty (and they're out there), then they're already more pissed at Meggs for letting JW walk outright. Meggs knows that. He's been around there for a long time. He's not even really a prosecutor. He's just a politician and the boss. The people that work for him are the ones that try the cases if they're to be tried. His call, but they informed his decision.