One true male deity, stern but loving, created the universe,
That's what you get in a monotheistic religion, one true and perfect God.
cast those who rebelled against him out of Heaven and they went down into to Hell, only by repenting and accepting the forgiveness of God can you cast off the Taint (i.e. original sin) and redeem yourself in the eyes of God and get to Heaven (i.e. accept Jesus as your personal savior)
Elrism claims that the Delmai were cast out of Heaven, however they could never redeem themselves. They are Elrin's enemy and later willingly occupied hell.
The Taint in Elrism is best described as humanity being corrupted by the Delmai, and is also used to create a natural distance between nobility and peasantry.
And as in every religion of BM, serve God well and receive salvation and eternal life in the presence of God.
god created the Delmai (i.e. angels) to shepherd humanity, the Delmai revolted against god whereupon he cast them down,
Angels are the messengers of God, to carry out God's will, including shepherding humanity. But from what I know, God never banned the angels from Heaven. But correct me if I'm wrong.
To me it seems Pelgart wanted to create an antagonist of Elrin. And it would be illogical for Elrin to create powerful deities to be His enemy. So, he created powerful shepherds who became power hungry in the absence of Elrin, and upon His return He cast them out, subsequently creating the antagonist. Good RP if you ask me.
if you commit a sin you have to make an Admission (i.e. Confession) to a priest, etc., etc. ...
In every religion you see that those who acted contrary to God's bidding will seek out priests to make amends for their sins.
From such a point of view, every earthly monotheistic religions are strikingly similar to Christianity, and that alone would make your criticism moot.