The only "power" in question is rationality (freedom from natural laws, both in perception and action). A nice summary of the distinction of faculty vs. mere receptivity can be found in the Anthropology, § 7. The categorical imperative and kantian morality in general does not take into account any factual (empirical) power or equality, but moreso faculties and intention.
One of the best textbits to illustrate that:
Even if by some particular disfavour of fate, or by the
scanty endoent of a stepmotherly nature, this will should entirely
lack the capacity to carry through its purpose; if despite its greatest striving it should still accomplish nothing, and only the good will were to remain (not, of course, as a mere wish, but as the summoning of all means
that are within our control) ; then, like a jewel, it would still shine by
itself, as something that has its full worth in itself. Usefulness or fruitlessness can neither add anything to this worth, nor take anything away
from it. (Groundwork, Ak. 4:394)
That means that when you are a peasant and can factually not do something morally good because it is not in your power to do so, you are still moral as long as you do everything that is in your power. And when you have the factual power to do good in the world and do not act with good will, i.e. e.g. respecting the dignity of every rational being (see Groundwork, 4:429-433), your are in fact immoral.
Peasants have rationality and therefore dignity, animals may have it, but it is hard to tell. He himself, in the spirit of his time, adapts the juridical view that animals in practical affairs are to be treated as things. Only exception being in the Metaphysics of Morals, where he argues that being cruel towards animals dulls your ability to be empathetic, which is something that you cannot rationally want, hence it is immoral (6:443; Part 2 §17). And making it categorically immoral to let animals suffer is surely ahead of his time.
PS: If you want to learn more about the political implications of the categorical imperative, I suggest reading his Towards Perpetual Peace, where he explicitly writes e.g. that there is a need of republican constitution that guarantees the freedom of all individuals (8:349-50). He writes about how to use political power in a moral way, too: He distinguishes between a political moralist, arguing that whatever he does is right as mean to a certain end (i.e. what he likes to do), and a moral politician, using the categorical imperative as a minimum standard of political action and doing what is right, not what he likes to (8:377-8).
