I think in the following sentence:
Adam's answer was similar to that of clergy.
"That of clergy" can be replaced by "clergy's" or "clergy's answer":
Adam's answer was similar to clergy's.
So, if my understanding is correct, can we say the following two sentences are grammatically equivalent too?
This is my book.
This book is of me.
Since in the first sentence, "of clergy" was indicating possession, I expect "of me" to mean "mine" and indicate another form of possession too.