@Trizek-WMF the blue border appears in some other cases of UI elements (i.e. Legend expand link).
|Open||None||T172250 Reconsider the blue border for buttons themed like links on focus/click|
|Open||None||T172578 Investigate and consider keyboard-only focus for OOUI widgets|
Frameless buttons, in general, are supposed to be frameless, and they're usually inside other elements that don't take into account the "box" that is around them. The frame that appears on focus looks weird and abrupt on these types of buttons, especially when they're in the middle of some other box, which these type of buttons usually are.
I can understand the need to make them look focused when the focus is on them but maybe the current design is quite a bit too thick and emphasized. It would be better, in my opinion, to make a much less abrupt indication, like we do with hover.