Rune Cap
Just a display bug. You are not getting the bonus stats from your PVP gear, however the UI will display it and make it look like you are. It has been a known bug since launch I believe.
https://forum-en.gw2archive.eu/forum/support/bugs/A-question-about-runes
https://forum-en.gw2archive.eu/forum/support/bugs/Superior-Rune-Slot-Display-Bug
https://forum-en.gw2archive.eu/forum/support/bugs/Rune-of-the-Ranger-bug
https://forum-en.gw2archive.eu/forum/support/bugs/Superior-Rune-of-the-Mesmer-7-6
https://forum-en.gw2archive.eu/forum/support/bugs/Changing-of-Armor-Runes
https://forum-en.gw2archive.eu/forum/support/bugs/Superior-Rune-of-The-Soldier-is-broken
https://forum-en.gw2archive.eu/forum/support/bugs/Superior-Rune-of-the-Pack-2
https://forum-en.gw2archive.eu/forum/support/bugs/Equipment-Bugs
to name a few it’s a known bug
no this will not benefit stats in any way..
it’s just adding the numbers on same runes is all