I think it's generally better if you limit the number of religions that have access to any given power, so those religions feel more unique. The more ubiquitous features are, the more bland and samey each religion becomes. Already many of the religions in EK feel rather bland, having the Mer be the only ones with ancestor worship would help make them feel more unique. That said, this shouldn't mean that should be the only ones that have it, but as long as the Eight/Nine divines and daedra cults don't, that's enough to help set them apart.
Even if it isn't sainthood/venerated ancestors, there should be different mechanics and features for the mainline religions to keep them from feeling the same.