I did not think the rivalry was friendly as a kid. Anything but. I was tormented and teased by BYU fans even though I lived in Utah’s backyard. It was that behavior that personally drove me to hate BYU. It wasn’t Urban Meyer and some urinal cakes. Utah fans hated BYU long before that.
What has made the situation different for BYU fans is that Utah is now the dominant team. So Utah fans feel more emboldened to tease or criticize BYU fans. BYU fans feel worse because it sucks to take abuse and lose.
But if you were to ask a Utah fan if they think the rivalry is friendlier or worse now than it was 30 years ago, I bet they would say friendlier. It’s just a matter of perspective.