Jonathan Last argues no. He tallies up Romney's mixed record of winning elections in Massachusetts with his poor record during the 2008 primaries, and concludes:

I’d argue that his electoral prospects are even worse than they look from his won-loss record. Here’s why:
(1) Romney made his political career out of his “close” 17-point loss to Ted Kennedy. But keep in mind that to only lose by 17, he spent $7M of his own money. But more importantly, this was the 1994 midterm election—so he got blown out during the biggest Republican wave in half a century.
(2) The high-point of his electoral career was the 2002 MA governor’s race, where he took 49.77%. Even in the biggest win of his life, he couldn’t capture more than 50% of the vote.
(3) It’s funny that Romney’s line of attack on Perry seems to be that Perry is a “career politician” because he’s been in elective office since 1984. Well, Mitt Romney would have been a career politician too, if only voters would have let him. He’s been running since 1994. His real gripe about Perry is actually, “Hey, that guy wins all the time! No fair!”

I think this is somewhat unfair to Romney. Running as a Republican in Massachusetts is hard. Rick Perry couldn't win statewide office there if he were running against Lee Harvey Oswald. What's more, Last tallies up Romney's primary record as if each race were a separate election. In reality, the primaries are all connected with each other, and a loss in one place makes further losses more likely.

Still, he's not wrong about the big picture. Romney has trouble attracting core supporters because he is so transparently political, as Scott Galupo explains:

You can practically hear the clanging and buzzing of Romney Robotic Manipulation technology:
What are Rick Perry's political weaknesses?
Ding!—Extreme rhetoric on constitutionality of Medicare and Social Security—Beep-Beep-Ding!—From border state; soft on immigration—Ding!—[Making necessary adjustments in left hemisphere of RomneyBrain]. ...
flip-flopping isn't necessarily a fatal flaw. It's when voters trust neither your flip nor your flop—that's when you're toast.

Flip-flopping isn't fatal. But it is true that voters make broad judgments about politicians that amount to more than a mere tallying up of issue stances. The best politicians create a successful persona.

I think Romney is a below-average presidential nominee, but that this has been obscured by the competition, which he towers above. Rick Perry would be a really bad nominee, and Michelle Bachmann a horrible one. In 2008, I considered Romney the weakest possible nominee of the Republican field. Now he's the strongest, and not because he's done anything better. To put it differently, if the 2008 version of John McCain -- the popular war hero whose many breaks against the Bush administration were fresh in voters' memory -- were the nominee, he'd be a very strong favorite to win.