I'll be honest. I like the newest approach to rivens.
The most powerful/popular weapons don't need help from rivens to do their thing.
Starting newly released weapons at minimum disposition makes all kinds of sense. Being new, they are going to be popular as a novelty. Time will tell how popular they remain. And it reduces wild fluctuation in value of their rivens.
And regular updates to disposition can only be a good thing for all weapons, but the new ones in particular as they find their 'level'.