Why shouldn’t Ceres be a planet? If Pluto gets to be a planet then Ceres is definitely a planet.
But there is still active geology on Mars. There is still moisture, winds and ice-caps that are shaping the environment. I consider that to be geologically active.
EDIT: And there are actual experts which consider active geology (or something similar) to be a planet, including Anton Petrov (https://www.youtube.com/watch?v=8-2HxrgqUnM)
Okay, but then you have to go and figure out which other asteroid and kuiper belt objects are planets.
The 'dwarf planet' distinction helps solve this! There are planets - distinctive in that they have clear orbits - and there are dwarf planets, which can be part of belt systems. This is a useful distinction.
Sure it is, but the distinction between terrestrial planets and gas giants are also useful, that doesn’t mean the latter aren’t planets.
I think it is fine that there are more objects planets then we can meaningfully count. Loads of things in our language act like that. E.g. a bug can be any number of things, and you know what a bug is by just talking about it. If some insect society then comes up with a meaningful definition of bugs which excludes spiders, that definition isn’t really doing the average user of that word any favor.
But there is still active geology on Mars. There is still moisture, winds and ice-caps that are shaping the environment. I consider that to be geologically active.
EDIT: And there are actual experts which consider active geology (or something similar) to be a planet, including Anton Petrov (https://www.youtube.com/watch?v=8-2HxrgqUnM)