Are all rabbis created equal? No. Some rabbis are more expert than others. The acquisition of rabbinical certification does not imply mastery on all matter of Torah. Some scholars have attained higher levels of expertise and there are leading scholars who simply know more than almost all others. This is as it is in all fields of knowledge.
R. Chaim Jachter quotes a number of sources on this in his Gray Matter volume II, p. 192:
[T]he beit din must not allow rabbis of ordinary stature to rule on matters of great complexity or import (see Teshuvot Meishiv Davar 4:50). For example, the Noda Biy'hudah (vol. 2, Y.D. 88) criticizes an ordinary rabbi for ruling on a case of ro'eh machmat tashmish, a complex area of the laws of family purity that can potentially result in forcing a couple to divorce (see Shulchan Aruch, Yoreh Deah 187). Rav Moshe Feinstein (Teshuvot Igrot Moshe, Even Ha'ezer 1:64) similarly writes that ordinary rabbis should not rule on matters of contraception.(see here for another post on this)
 Regarding the pervasiveness of this problem in our generation, see Nishmat Avraham (4:13-16) and Rav Tzvi Gartner's essay in Tradition (32:3:94-95). See also Pitchei Teshuvah (Y.D. 99:6).