Why higher aperture for Astro?

Hi everyone, I’m getting into astrophotography with a Nikon Z 6 III setup and I keep running into something that feels like a contradiction — maybe I’m missing something obvious.

From everything I’ve learned so far, faster lenses (f/1.4, f/1.8) should be better because they let in more light. That should mean lower ISO, shorter exposures, and overall cleaner images — which sounds ideal for astro. Especially when you have low light like for Andromeda (thats my goal).

But then I see a lot of recommendations (even “premium” ones) pointing toward f/2.8 lenses — especially zooms like a 14–24mm f/2.8 — instead of much faster primes.

So here’s where I’m confused:

• If light gathering is so important, why not always go for f/1.4 or f/1.8?
• Why are some f/2.8 lenses considered better for astrophotography than faster lenses?
• Is the trade-off mainly about image quality (coma, sharpness, etc.) at wide apertures?

From what I understand, a lot of very fast lenses don’t perform well wide open and need to be stopped down anyway — sometimes close to f/2 or even f/2.8 — which kind of defeats the purpose of buying a super fast lens in the first place.

So is the real priority something like: image quality (coma correction, edge sharpness) > aperture speed?

Wjat you think ist best for low light Performance (Andromeda / Milky Way)

Thanks!