While far be it from me to defend the IAU, that is just nonsense. If anything we need better definitions and more categories and the IAU got the ball rolling on this.
What the IAU "got the ball rolling on" was chaos. They had a bunch of astronomers telling planetary scientists to use a definition that they disagree with. Many have taken to just ignoring it, in the peer reviewed research. To give two examples of how absurd the definition is: 1) the definition states that something is only a planet if it revolves around the sun, not other stars - and yet the IAU has an exoplanets working group. Exoplanets aren't planets! 2) The concept that "a dwarf X isn't an X" is not only linguistically absurd, it's a view not even shared by the IAU itself, which is more than happy to consider, for example, dwarf stars to be stars.
The main reason stated by most astronomers who backed the decision is almost invariably (seriously, read interviews with them), "I don't want my daugther having to memorize the names of sixty different planets". As if that's even slightly a valid reason for making a scientific decision.
Jupiter and Earth bear almost no resemblance to each other and yet they both are planets.
Exactly! And yet rather than kick the gas giants out, they kicked out another solid body that has far more in common with Earth (including, I should add, active geology and weather) rather than the bodies that have almost nothing to do with Earth.
In reality they should probably be different categories of entities. We used to consider Ceres a planet a long time ago
And we should. Believe it or not, because some scientists in the 1800s changed their mind about something doesn't mean that this is some sort of eternally correct decision. They had no clue about the concept of what bodies would end up in hydrostatic equilibrium and the consequences thereof.
Let's go to biology. We label species all the time based on location and proximity to other similar animals rather than the much simpler "can they mate" question.
How do you see this as even remotely similar? If you take a shrew from Ohio and you place it in Nepal, does it cease being a shrew and become a dwarf shrew that no longer counts as a shrew?
Or geography. We label mountains and bodies of water precisely based on what they are next to. You could reasonably consider the Mediterranean Sea as a part of the Atlantic Ocean if you really wanted to.
So because it hasn't "cleared its neighborhood" does it suddenly become the Mediterranean Pond despite being a size that we traditionally call a sea? Do we arbitrarily declare that there's only 8 mountains in the world and all others are "dwarf mountains" that aren't really mountains because we think there's too many mountain names for kids to memorize?
Umm, ok. Presuming that is true...
Seriously, you're going to cast doubt on the guy who came up with the Stern-Levison parameter that's used to make that distinction?
It would be equally true to say that Earth wouldn't be a planet if it wasn't orbiting the Sun but equally irrelevant as well because it manifestly does.
Right. Because it totally makes sense to have an perfect copy of Earth orbiting in a larger star's habitable zone (and thus have a lower Stern-Levison parameter) not be a planet while its perfect copy is.
Pluto is very much like Ceres and other big rocks
Pluto is absolutely not "much like" "big rocks", and the fact that you'd make this claim is a profound expression of ignorance on the topic. And should I add, one of my greatest peeves about the IAU's decision. Since their discoveries long, long ago both Pluto and Ceres had been nothing more than specks, dots of light. We knew next to nothing about either of them. Then finally, at long last, right before we were about to get real data on both of them, rather than even waiting for the data to arrive, they decided to make declarations about them. The most unreasonable time they could have picked in a century to do so, that's when they did it. And don't even get me started on how the vote went down...
Pluto is about as different from a "big rock" as you can get. Pluto has an atmosphere. With apparently complex nitrogen photochemistry and clouds going on in it. With snowfall and frosts, and a chemically diverse surface. And glaciers, carving out canyons. And signs of what appear to be flowing liquids of an unknown nature in the past. And cryovolcanoes. And tectonics. And types of terrain we don't even have a clue what they are. And the incredible Sputnik Planum, something never before seen in our solar system: effectively a planetary mantle exposed to the atmosphere, an area devoid of crust where the underlying eutectic-ices slowly roil on the surface in supermassive convection cells, with icebergs the size of mountains riding around on top of them and collecting on the shores.
This is what you call a "big rock"? It's a heck of a lot more geologically interesting than half the "planets". And absolutely nothing like the sort of primitive, unaltered, inactive bodies that it's now lumped in with.