In aggregate I probably agree but one thing I've wondered, especially in the last year as I started gardening during lockdown, is if that's really universally true. Large, long-lived plants - redwoods, oaks, saguaros, and so on - seem very close to the same niche in the plant kingdom humans occupy in the animal one. They exert significant energy to cultivate and modify their environment; they gather and store resources they do not immediately need; they change "behavioral" patterns significantly and cyclically over the course of their life; they maintain vast communication networks.
I have no doubt a pig "outranks" a mosquito. But I also suspect a redwood outranks a mosquito. The middle is all fuzzy though - where does my cucumber (which exhibits relatively complex reproductive behavior to attract pollinators, and expresses significant "wants" in terms of vining and leaf facing) lie in relation to mosquitos, or aphids, or bees?
You've made interesting points, but I think the most important point here isn't one of biology but of moral philosophy: animals presumably outrank plants in terms of moral standing.
Torturing a person is presumably worse than torturing a mosquito. A person has more capacity for pain than a mosquito, and in turn the mosquito has more capacity for pain than does a heap of sand.
I figure plants lie further down the ranking than mosquitoes, for the reasons you've just explained. They're certainly further down than farmyard animals. It would be considerable moral progress to switch from torturing billions of chickens and pigs, to torturing billions of plants (and that's ignoring that a plant in a farm environment is likely 'happier', in its own terms, than a livestock animal).
A vaguely related TED talk on how brains ultimately exist to orchestrate movement, and essentially nothing else: https://youtu.be/7s0CpRfyYp8?t=15