That’s true. As a universalist I would argue that there are different terms to describe essentially the same thing.
Interestingly both the Vaishavite Hindus and Christians have a belief in Krishna and Christ as being incarnations of Vishnu/God.
Generalizing things in the other religions is one of the problems that Baha'is are susceptible in doing. To become "enlightened" or to become a "sage" in some religions is something that any person can become. It might take many lifetimes to achieve it, but they can do it. A "prophet" in Judaism seems way different to me. These people were chosen by their God to deliver a message. A "manifestation" is even more special and unique... if it is true. Those people are supposedly "perfect" mirrors of God?
And that's a problem for me believing the Baha'i explanation. As we talked about all ready in other threads, all the patriarchs in Judaism are very human, with imperfections and faults. Some of the prophets in Judaism like Samuel, Jeremiah, Elijah and Isaiah, to me, would be closer to fitting the description of "manifestation" than even Abraham or Noah and especially Adam. And then we have David, the Lord's Anointed King. He made so many mistakes, yet he was called the "apple" of God's eye?
Then the problem of religions that make their prophets/founders/manifestations into God/men. Baha'is have to disagree with these kinds of claims and find alternative interpretations of the religion's Scriptures that say or imply that those people are "God in the flesh" or some kind of incarnation of a God. Re-interpreting verses is already a problem, but then Baha'is also say that the Scriptures aren't "authentic" and have had "traditions" added in. Which makes the Scriptures of that religion, not the "Word of God", but the word of men. Which, if that's what Baha'is really said in the first place, I'd be fine with it... That all the previous religions were men's attempts to understand an unknowable Spirit Being, and they were all wrong. That some traditions they came up with had some benefit to people and civilization, but many rules and practices weren't all that good and needed to be replaced and done away with... like animal sacrifices, stoning people for breaking the Sabbath, sacrificing people to the various gods etc.
So did the real God order people to obey those kinds of rules? Did God ordain those kinds of practices? I don't think so. So then, where did those things come from? I'd have to believe it came from the leaders of the people. People made the rules of their society and defined their religion and their gods. I don't see it didn't coming from the "real" God in some "progressive" way that slowly evolved over time as people advanced. For me, right now, the Baha'i explanation is too simplistic and over generalizes religious evolution. I think man had much more to do with it then God.