What I've heard is that both are very important...
However, there's so much to take into consideration when it comes to GPA: grade inflation, deflation, the competitive nature of your undergrad university/college, grade trends, etc. B/C of this, I've heard that there is a growing discrepancy between GPA's and that not all like GPA's are equal. Therefore, many of the med schools look at the MCAT as the "equalizer". Being that it's a standardized exam, everyone has a fair shot at it and your scores can really reflect your ability to take on med school.
Correct me if I'm wrong...😉