The only reason P&W get blamed for anything is snobbery. Those who drooled at the idea of an Oscar-nominated writer handling the script are snobs. A non Oscar-nominated writer could well turn in a script which is equal or perhaps even better than what Logan does.
Well that's just a little patronising!
The reason i personally was happy to have Haggis on board was because he'd recently written two very solid scripts, Crash and Million Dollar Baby, whereas P&W had recently written DAD.
Talking about snobbery may well fit your argument, but i'm afraid you're going to have to give a little more credence than that to the opinions of others.
Your derisive comments on P & W are, of course, welcome since they are your opinion. But on a message board opinions tend to get challenged. In that spirit, if you keep on blaming P & W for your displeasure with DAD, contrasting it with Haggis´ "Crash" (a very controversial choice, by the way, since so many hated that film) and "Million Dollar Baby", you should also take into account that Haggis contributed scripts for "Walker, Texas Ranger".
Had Haggis been the show runner, like on Due South, then we could perhaps pin him with the blame for the overall quality of Texas Ranger. But the Walker scripts, if I remember this correctly, were done as a favour to a mate. It was essentially a work for hire gig.