A5E expertise die are at a basic level a replacement for the 5E D&D expertise double proficiency skill bonus. It is a bit more complicated than that, but that's a significant portion of it. Expertise die stack, d4->d6->d8 maximum, unless you have certain class features like the Rogue to go beyond d8.
One very good thing about A5E is that all the classes have some good utility features, so there's more that everyone can do outside of combat. In that sense, A5E did improve utility capability of many of the classes, so you can consider it a power up in that sense. That said, I've played both 5E D&D (2014) and A5E, and I haven't found A5E to be over-powered, either from a combat or utility view point - I would just say that it is more balanced outside of combat.