Maybe one problem is Baha’is thinking sometimes that all religions are one, and trying to find some way for that to be true, which it isn’t. Also sometimes people might think that “all religions are one” means “all religions are equal,” and that might always be what Baha’is mean when they say that.
The key here is that the Baha'i Teaching say that it is the Foundation that makes Religion One. Abdul'baha explained this in many talks in many ways.
Here are a couple;
"In further consideration of this subject, I wish you to be fair and reasonable in your judgment, setting aside all religious prejudices. We should earnestly seek and thoroughly investigate realities, recognizing that the purpose of the religion of God is the education of humanity and the unity and fellowship of mankind. Furthermore we will establish the point that the foundations of the religions of God are one foundation. This foundation is not multiple for it is reality itself. Reality does not admit of multiplicity although each of the divine religions is separable into two divisions. One concerns the world of morality and the ethical training of human nature. It is directed to the advancement of the world of humanity in general; it reveals and inculcates the knowledge of God and makes possible the discovery of the verities of life. This is ideal and spiritual teaching, the essential quality of divine religion and not subject to change or transformation. It is the one foundation of all the religions of God. Therefore the religions are essentially one and the same." Abdu'l-Baha : Baha'i World Faith - Abdu'l-Baha Section
Also about Christ and what we can expect to see from a Valid Messenger,
"Christ ratified and proclaimed the foundation of the law of Moses. Muhammad and all the prophets have revoiced that same foundation of reality. Therefore the purposes and accomplishments of the divine messengers have been one and the same. They were the source of advancement to the body-politic and the cause of the honor and divine civilization of humanity the foundation of which is one and the same in every dispensation. It is evident then that the proofs of the validity and inspiration of a prophet of God are the deeds of beneficent accomplishment and greatness emanating from Him. If He proves to be instrumental in the elevation and betterment of mankind, He is undoubtedly a valid and heavenly messenger." Abdu'l-Baha : Baha'i World Faith - Abdu'l-Baha Section
Regards Tony