I read it as, across the board a 1% performance improvement. Not that only 1% of packages get a significant improvement.
In a complicated system, a 1% overall benefit might well be because of a 10% improvement in just 10% of the system (or more in a smaller contributor).
The announcement is pretty clear on this:
> Previous benchmarks (...) show that most packages show a slight (around 1%) performance improvement and some packages, mostly those that are somewhat numerical in nature, improve more than that.
In a complicated system, a 1% overall benefit might well be because of a 10% improvement in just 10% of the system (or more in a smaller contributor).
The announcement is pretty clear on this: