Beginning at my normal medium speed, I was asked after cohen to pick up the pace because otherwise the men would miss their train to work. At that place and time, normal-speed leining was a tircha de-tzibura! If I were saying a “voluntary” kaddish, I’d bear this in mind.
Maybe your leining really is medium, but everyone probably thinks their pace is average, but not everyone’s is.
The comparison is far from great anyhow, because the minyan must anyhow account for Kaddish, but not for a slow (or relatively slow) leining.