Yeah this is the correct take. Either Pluto (and by extension, any object of similar size) is a planet, which would mean there’s thousands of Pluto-sized planets in the solar system; or pluto is ‘too small’ to be a planet. Which is the answer they (Sci community) settled on, because if every comet/asteroid is within the threshold definition of ‘planet’ then there would be no point in distinguishing planets at all.
Kinda like how we have dwarf-stars and supermassive stars 1000x bigger than our sun. If they were all the same size there would be no point defining them beyond ‘star’.
That’s pretty much how it is. In ancient times, planets would have been objects that were distinguishable from stars in ways they had the ability to differentiate from. For example, with a telescope, any object that doesn’t shine like a star, that moves across the sky at a different rate than the stars, or maybe has visible rings.
Then once science found things that past science couldn’t account for, they redefined what a planet was, according to its size/gravitational pull or other factors, and which Pluto didn’t fit. Apparently due to Pluto’s small size, it’s not even a dwarf-planet, and by that measure is basically just a really big asteroid (we even know of asteroids that are bigger than Pluto).