Why do you think that? That would be circular reasoning. Moreover, anyone can make claims, as many false prophets do.
Baha'u'llah never said that His claims are the evidence that His claims are true. Rather He said:
“Say: The first and foremost testimony establishing His truth is His own Self. Next to this testimony is His Revelation. For whoso faileth to recognize either the one or the other He hath established the words He hath revealed as proof of His reality and truth. This is, verily, an evidence of His tender mercy unto men. He hath endowed every soul with the capacity to recognize the signs of God. How could He, otherwise, have fulfilled His testimony unto men, if ye be of them that ponder His Cause in their hearts. He will never deal unjustly with any one, neither will He task a soul beyond its power. He, verily, is the Compassionate, the All-Merciful.” Gleanings From the Writings of Bahá’u’lláh, pp. 105-106
I see that the Person, the Life and the Words are the substance of the Claim, or in other words the evidence of the Claim.
The Claim is supported by those 3 aspects. So a Messenger is their Claim, the claim is judged by that evidence.
The False Messenger is the substance of their Claim.
So maybe we same the same thing in a different way. I am also just thinking is not creation circular? For instance can the seasons be seen as circular, the sun the planets the universe in a constant circular motion? The cycle of Revelation?
Regards Tony