The arbitrary cutoff size being to ensure continuity of the scientific consensus in popular awareness when I was a child isn’t a stupid rule.
Not even when a larger kuiper belt object is found.
Not even, when since mass is the primary means of estimating size until we fly a probe out there, we estimate a smaller but much with much more mass object to be larger and we debate a 10th planet yet again.
You’re not wrong, but I’ve also seen people calling Pluto-Charon binary dwarf planets.
But yes, the IAU tends to only pin down definitions when one is becoming unworkable - in this case the ever larger numbers of trans-Neptune objects that were potential planets.