Yeah, I'm really not understanding this.
I wish this to be the case, but Bungie hasn't said they are going to address it. They haven't said anything about the 25-28 gap that I know of.
I wouldn't imagine that "Brand New Rare Items!" are very high on their list of PR talking points. It'd be relatively simply to just shave a few perks off the old Legendaries and turn 'em blue.....or just add more Light to old Blue Items. We shall see.
In the meantime you can make up the deficit somewhat by killing the Devil Walker out in The Divide once a day. The daily reward for Public Events should be fixed in Dark Below.