While I agree with you on most points, that is not why Pluto is not a planet.

The reason is that it was observed "too soon" because of its interaction with Neptune's orbit. Once we realized there were plenty of such objects in the range of Neptune's orbit but we also realized that these were not fully formed planets, we invented the term of dwarf planet, so Pluto was demoted to that status, which it shares with many other objects in the far out orbit.

So, it was just a classification thing. We could have also said all those others are also planets.