Bahaullah is certainly not dismissing the Trinity as a false doctrine but acknowledging it as Divine reality.
"O People of the Book! Commit no excesses in your religion: Nor say of Allah aught but the truth. Christ Jesus the son of Mary was (no more than) a messenger of Allah, and His Word, which He bestowed on Mary, and a spirit proceeding from Him: so believe in Allah and His messengers. Say not "Trinity" : desist: it will be better for you: for Allah is one Allah: Glory be to Him: (far exalted is He) above having a son. To Him belong all things in the heavens and on earth. And enough is Allah as a Disposer of affairs. (Verse 4:171)
Abdul'baha has explained in detail as to what Baha'u'llah offered, in this explanation;
Some Answered Questions | Bahá’í Reference Library
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The Messengers are the 'Self of God' only as the Mirrior. All we see of them is the Reflection of God in Attributes. God is unknowable in Essence, even to the Messenger. This is a big subject and there are many avenues of thought to consider.