If Eidolon of Astral Winds enters at the same time as one or more other enchantments you control, its last ability will trigger for each of those enchantments, including itself.

The effect of Eidolon of Astral Winds's last ability will overwrite any previous effects that set the creature's power and toughness to specific values. Effects that otherwise modify the target creature's power and toughness will still apply no matter when they took effect. The same is true for +1/+1 counters.