The job description debate is a scratched record from October 2011, some is a near verbatim repeat of those posts from last year. It's tempting to delete them from here on ground of double posting 
Lets get back to reviewing the team's performance. Marcush & Morteza have led the way, here's my contribution....
I agree there was a glimmer of hope earlier this season, but it now looks like a rather sad deflated balloon.
One could say that there’s no shame in finishing behind McLaren, RB & Ferrari, but Lotus show that a mid-order team can rise to challenge the top 3. It's not as if Merc can blame a DDD-esque loophole for Lotus's rise, it's just hard work, good engineering and good strategies. It's also not much excuse considering the effort Merc have put into building the team.
The challenge is to sift the contributing factors. Bell, Costa & Willis had no input into the genesis of the current car, so they can't carry much blame for that. Where their input should be making a difference is leading the team and improving how the team functions and performs. I would hope that there are internal signs of more resilience at race weekends, along with a more resilient factory & development team. The signs may not show to external viewers, but internally they'll know if they are better at managing risk and change control, they'll know if they are making less mistakes, and those mistakes that are made are resolved effectively.
In a nutshell, I'd say the new recruits should be showing signs of improving efficiency and effectiveness this year, and that would manifest itself in a faster car next year. I hope they have some good evidence of leadership and better teamwork behind the screens, because what is happening on track at the moment doesn't look too good.