The pasuk itself simply has Hashem tell Avraham to look at the stars and count them, declaring that so shall his offspring be (Bereishit 15:5), without any stated reason tied to how stars are seen relative to one another.
Haamek Davar (Bereishit 15:5) reads the star comparison as being about stature and quality rather than mere quantity — Avraham's descendants would include many men of greatness who 'bring light' like stars, a point meant to answer his fear that his offspring, already compared to the dust of the earth, would be insignificant.
Malbim (Bereishit 15:5) develops this idea of individual significance: just as each star is its own world such that the loss of a single star would be a loss to all of creation, so too each individual of Israel is a complete world whose loss touches the wholeness of the entire nation — a point about the irreplaceable value of each person, not about stars avoiding outshining each other.
Or HaChaim (Bereishit 15:3) similarly explains that being compared to dust implies insignificant people lacking a holy soul, and that Hashem's answer of 'count the stars' was meant to assure Avraham that his descendants would each be important in their own right — again a statement about stature, not about relative visibility among stars.
Shem MiShmuel, Bamidbar 4:3-4 distinguishes the blessing of stars from the blessing of sand, reading the stars as representing quality and greatness (Avraham) and the sand as representing sheer quantity (Yitzchak), with the dust blessing to Yaakov representing yet another dimension — again this is about quality versus quantity, not about stars not outshining each other.
Alshich does bring a distinction between stars and the sun and moon, noting that stars have no shame, unlike the sun and moon of which Scripture says they will be ashamed and abashed — but this concerns the stars' freedom from future embarrassment, not the idea that stars can all be seen without one outshining another.
Midrash Tanchuma, Lech Lecha 3:4 addresses the broader promise of nationhood and creation language used of Avraham, but says nothing about the stars as a symbol of mutual visibility or non-rivalry among them.
Taken together, these sources do not bear out the specific idea that the stars were chosen as a symbol because they can all be seen without outshining one another; the explanations offered concern stature, individual irreplaceable worth, and quality versus quantity, as in Haamek Davar (Bereishit 15:5), Malbim (Bereishit 15:5), Or HaChaim (Bereishit 15:3), and Shem MiShmuel, Bamidbar 4:3-4, with Alshich touching only on the stars' freedom from shame.