Suhas, Ramakrishna did not have know about all religions, he had a superficial understanding of Islam and Christianity, so he is not qualified to make the statement all religions are true, because he is interpreting Islam and Christianity through Hinduism. He does not seem to realize that Islam and Christianity violently oppose his statement. Islam and Christianity do not believe all religions are true, they believe their way is the only way.
Swami Vivekananda was more educated than Ramakrishna, knew more about Christianity and Islam than he did, and he made many critical comments on them in speeches delivered to native audiences. He did not make similar comments when addressing Western audiences because it would have alienated them.