Solid, well defined principles that are followed as much as possible. Not more variables to an equation.
Who's going to enforce those principles and how?
The same way it is enforced now, only with less steps. The community, only we have a clear set of rules we all agree to follow as opposed to a murky equation with ambiguous terms and tons of exceptions.
Then what's wrong with the way it is? The system merely sets a default list but also encourages users to set custom lists.
Or is your suggestion to remove the default altogether? In which case all feedback would have the same weight, meaning the community would have to police all feedback and then someone would need to be granted the authority to remove "incorrrect" feedback or somehow prioritize those who tend to leave more correct feedback, which brings us back to square one.
There aren't that many steps in the system. DT hierarchy is selected via an algorithm (that's where most of the variables are but mostly to weed out alt farms and such; those variables don't affect trust directly) and then DT is supposed to police itself.