Checks are only supposed to be for things there is a possibility for failure for. So a Cleric of Pelor probably wouldn't need to roll to recognize a symbol of Pelor or to know about specific Rites of Pelor. Knowledge(Religion), and later Religion(Intelligence), would be for general knowledge of religions or more esoteric religious knowledge. Having Proficiency in Religion shows that they had studied it, but not all Clerics would be scholars that pursue even further knowledge of the subjects.

Couple that with the ability tied to skills in 5e are suggestions, and the checks absolutely can be altered depending on the situation. Religion(Wisdom) would be perfectly in-line for a Cleric to make if that would make more sense for the roll.