Astrology makes its predictions in a vague and personally flattering way as to overwhelm critical facilities. This is not very different in how religion uses the language of threats and social coercion to deliver doctrine over one's senses. In both cases it's a defeat of rationality (and sorry I dismiss your whole first paragraph as sophistry).
> (FWIW, the Catholic Church rejects astrology, not as some "competing" doctrine, but as a pseudo-science and a superstition [0].)
Russian Orthodox church also rejects astrology as a superstition, or rather manifestation of paganism which is a competing doctrine. It also blesses missiles with holy water.
You diluted "religion" into something basically like "belief". Religion is the belief in some supernatural power (and, I would add, that requires faith because there is no evidence). Believing in ideas, in "highest good" is not religion, although religions include them as part of their dogma.
> Man is a religious animal in the sense that, as a rational animal, he must worship something he takes to be the highest good.
This needs more solid arguments. As is, it’s obviously complete bollocks.
So, if we interpret astrology as something explanatory, and there is no strong rational basis for it, then that means it is unlike those religious traditions that are rationally defensible. If astrology is a practical art, specifically, if it makes predictions based on some correlation between the positions of the stars and planets and whatever else, and this correlation happens to hold, then astrology is a more or less predictive model. (The "whatever else" also matter, as you could call the science of tides a kind of natural astrology because the moon does in fact have an effect on the tides.)
(FWIW, the Catholic Church rejects astrology, not as some "competing" doctrine, but as a pseudo-science and a superstition [0].)
[0] https://www.newadvent.org/cathen/02018e.htm