I think you are reading Perry's problems a bit wrong, or at least not seeing the whole picture. While I agree that his toxic rhetoric and hard right positions, not to mention his poor debate performances hurt, what really crushed him were the few issues where he approached sane policy. The first problem was when he got hit on the HPV vaccine issue by Bachmann. Sure Bachmann is a kook and didn't know what she was talking about, but there is a lot of conservative opposition to HPV vaccine, just as there is to birth control, and the issue resonated with some religious conservative voters. The next issue to present a problem for him was border security. As Governor of border state, Perry has needed to take a more pragmatic approach to illegal immigration than is considered acceptable among GOP voters in other states. But the biggest mistake Perry made, the knock-out punch he delivered to himself, was calling his critics of denying in-state aid to children of illegal immigrants "heartless." To conservatives that just sounded way too close to "bleeding heart liberal" territory for comfort, and it killed him, and that was the point where he really took a nose dive in the polls.
I think you are correct that Perry's problems came from a fundamental lack of understanding how national politics differ from Texas politics, but it is not simply a matter of Romney being able to outflank him from the left. The peculiarities of Texas politics left Perry open to attacks from both the left and the right, depending on the issue. Personally, given the generally angry nature of the GOP electorate this year, I think Perry could have survived statements like accusing Bernanke of treason. It was the issues where he was vulnerable to attack from the right, coupled with the fact that he looked befuddled in debate performances that really sank his candidacy.
I don't think it's either/or. I think a big part of the problem has shown up in Perry's palpably poor numbers vs Obama and Republican elites doubts that he can sell nationally. But yeah, these are absolutely critical too. It's all of a piece.