x11-misc/i3blocks has a runtime dependency on || ( x11-wm/i3 x11-wm/i3-gaps ), however i3/i3-gaps is not needed to run i3blocks.
This seems like an old bug report.
I can confirm that there is no runtime dependency on i3 or i3 gaps.
With sway as a project, i3blocks can be used in multiple places. Hence losing this dependency allows people to run sway without having to compile i3.