HW was doomed due to 12th year GOP fatigue and a lame ecomomy. His foreign policy accomplishments were widely praised, but this wasn't the decisive issue in the '92 campaign against any challenger.
I wouldn't say those things necessarily "doomed" him. For one thing, had Bush not given in to the Democrats & raised taxes, then he wouldn't have cost himself a lot of his support & credibility. The impact of that alone on his loss was pretty significant.
Unknown as the 1992 exit poll didn't ask voters about their positions concerning the pledge, but we all know that not only did Buchanan repeatedly cited the pledge as an example of a broken promise in the primary, but then Clinton (the moderate that he is) cited the quotation & questioned Bush's trustworthiness. To suggest that his failure to keep the pledge wasn't a reason for his defeat would be unwise.
The pledge was part of it, but not enough on its own. The economy, a desire for change after 12 years of Republican rule (I think the Dems could've eeked out a win in 88 had someone stronger than Dukakis been nominated), and Bush running an awful campaign in 92, had more to do with Bush's loss than the broken tax pledge.
