This is technical discussion; not design discussion. Designers probably not needed.
We have a few ways of implementing the desired focus effect (2px ring around controls), including what we currently use: adding padding.
Padding is problematic and causes a lot of issues with inconsistency + gappiness.
Instead, we probably want to investigate the QFocusFrame. This does have one disadvantage: we can't use it in QtQuick, which means we'll have to abandon qqc2-desktop-style (at least as the default) if we want to use it in Breeze. Since we have qqc2-breeze-style, I don't see the value of handicapping Breeze's design in order to accomodate a giant hack.