There are dice rolls that do have serious consequences. You can talk your way out of fights, or you can end up becoming food for a mind flayer.

The ones that seem to have the least weight are things like lore checks. I've seen a few concrete lore checks and few that were simply implied. The result in those cases, at least from my experiences, have been flavor and didn't have any negative or positive impact.

The one thing they NEED to add in is an option for the party members to interject (for good and for bad) in conversations. So they can either make a bad situation worse, a good situation better, or maybe even keep a situation from plummeting to the bottom of the abyss. They need more interactivity to happen in conversations, things like being able to sway a conversation with options to hand over goods or the like, during the conversation.

As to changing how the dice rolling system works, there are legal issues here. They don't OWN the setting, so they have to use the rules set the owners say they have to use. And when they have to make adjustments, they need permission. And something as core as how you define success would be one of those "need permission" sort of things.