There is a general dispute in taxonomy between "lumpers" and splitters" - people who say "this, this and this share these characteristics, and so I lump them together in one taxon" versus
those who say "this, this and this differ in these characteristics, and so I split them into these taxa".
You're evidently a splitter. No disrespect about that - it's a defensible position (see above). But being a lumper is also a defensible position (see above).
The important things that you need for designing a taxonomy are to know what questions you want your taxonomy to address - if you're wanting answers to questions of surface gravity, then a taxonomy based on colour is unlikely to be helpful, for example.
Our current taxonomy for planets is based on the observational status of the planets in respect of their neighbours - the "cleared orbital region" criterion. In principle, that is an addressable question - observe the skies, plot the orbiting bodies down to a few percent of the size of the planets of interest, question answered.
Where things are getting confused is that many people project questions of the origin of the planets onto the orbital classification. Which may not be the most logical thing to do, when looked at in the context above. The two questions are not strictly related : Earth, Venus, Uranus and Pluto all appear to have suffered a giant impact in the late stage of their construction, but Pluto does not currently have a cleared orbit to make it a "planet" under the orbital classification. So our believed-to-be-correct models of origin processes do not (necessarily) align with current orbital status. But you can see from the length of my qualifications above that one taxonomy split is based on fairly long chains of cause and implication, and the other on simple Newtonian mechanics. So I can understand why the IAU decided to go with the relatively simple present-day orbital status criterion.
If I were to design a planet taxonomy, I'd use a criterion of sphericity (is the shape within X% of being a simple spheroid) to divide planets from "minor planets" (you can look at it as the interplay of material strength versus object mass, if you like), and at the upper boundary the presence of fusion (separating planets from stars, with a fudge area to deal with brown dwarfs). But that criterion shows my interest in body materials (I'm a geologist by trade), which differs from the interests of astronomers in general.