Well said TI Rider.
Simmons couldn't beat out Simoneau, this year just as Danny Clark couldn't beat him out last season. It has very little to do with "play favorites" as opposed to Simoneau's strengths are his intelligence, his awareness on the field and always being in the position he was supposed to be in when the defense is called.
His physical limitations are what really frustrates the fans here... and as you noted, poor DL play really exposed him.
Simoneau isn't going to blow people up a la a Brian Urlacher, but there is a reason why he's lasted so long in the league. He's a good guy to have on your team because he always knows his assignments and executes them consistently -THAT'S what endears you to coaching staffs.
We've had linebackers that were more talented than Simoneau playing under Haslett, but all too often they were out of position, which caused the Saints to give up plays they should have had covered.
A classic example of a talented player who consistently blew his assignments was Tebucky Jones. I'll never forget the game agaisnt the Vikings on ESPN (Mike McKenzie's first game with the Saints), where the Vikes picked up a first down near the end of the game, and they cut to little Rasputin (Venturi) and he is furious because Jones decided to freelance instead of sitting on the route, preventing the 1st down.
Parcells wants Simoneau for that reason... he's a player who can organize his defense on the field and a reliable one while he rebuilds his team. He's not going to field a contender yet, he just needs someone who knows what the heck he is doing...