Mitt's one advantage is that he's facing off against a bad President in a bad economy. If he was facing Bill Clinton in '96, I'd agree with you. I'm not ready to write of Romney's chances quite yet. Yes, he's going to lose conservative votes. The question remains is whether or not he'll be able to pick up the middle that voted for Obama and are now unhappy with him.
We have a political system that works with people in groups ~ and those groups affiliate with one or the other of the two great political parties.
In numerous European countries they work it the other way around so you end up with dozens of political parties representing broad general interests or socio-economic classes, and they do their coalitions AFTER the elections.
Our system works to deliver us a fairly evenly divided electorate ~ so that you get a landslide if you get as much as 53% of the vote.
Outside of the two coalition parties there is a thin fringe of unaffiliated people. It's not a broad middle ~ more like a desert.
LBJ used that model in mind to win in a landslide against the first guy who'd proposed it ~ Goldwater! Nixon used it to win twice. Ronald Reagan used it to win three times (two times for himself and once for GHWBush). Bill Clinton won with that model ~ twice, while crushing a third party attempt. George Bush pulled it off as well.
All Obama has to do is hold the Democrats together while Romney himself delivers up the equivalent of a faction to the Democrats ~ in the body of people who simply aren't going to show up if Romney is on the ticket.
You can run anybody but Romney and beat Obama, particularly if he can attract that 53% of recent (Last 5 years) college graduates who are UNEMPLOYED.
From lurking on the Democrat sites, (know your enemy), there are as many disallusioned with Obama as there are Republicans with Romney's win...but they seem to be able to "live with" Romney as they see him as slightly less than Obama...so I agree it's a factor in the equation.... it could very well offset those refraining from voting for Romney.
As for Independants...they are either Liberals or Conservative, though you'll never hear them admit it....but I'm under the impression they will generally go with whoever is most liberal....however, Romney is liberal enough so I see them as leaning his way.
Obama's going to target easily led students and the less well off....he knows how to "organize" and bring in those votes.