I can see how that might sound like a claim, if you do not include what I said before that:
I believe that the true Messengers of God met their burden by providing evidence that supports their claims.
I think this is where a lot of the difference lies or a lot of confusion might also be.
Normally we would structure our thoughts or argument like this, to just simplify it:
1. (Experience/Exposure) We are exposed or experience something, and this could be anything from simply seeing or hearing something, to a deep or thorough research into a given topic.
2. (Belief) From that we shape our belief. For instance "I believe in UFOs" because I have experienced or been exposed to something which convinced me that this were true.
3. (Argument) From here I could get into an argument with someone about why I believe this to be true. And I could draw on (1) to create my argument and use this to create claim statements. And this person could question these and we could have a back and forth about them. But I wouldn't draw on (2) and this person couldn't really argue against my belief, because it is obviously arrived at from something else, the belief itself is passive so to speak. Equally you couldn't argue against whether "I like red more than blue". But if I claim that the reason for this is because red is much better for our health than blue or some other none sense, you can "attack" that claim.
Obviously this is a circular approach, because (3) is basically also (1) the Argument step is also us getting experience or exposure to something and this might make us change our belief. If you demonstrate to me that my argument about "red being healthier than blue" is wrong, I might actually change my belief.
So in your case, the discussion or argument is not whether you believe Baha'u'llah is right or wrong, because clearly you do. But whether or not they have met the burden of proof, which ultimately convinced you that this is the case. In which case, you would have to present an argument for why this statement:
1) Their Person (their character, as demonstrated by the life they led)
Would or could lead to the conclusion that Baha'u'llah were telling the truth. Its obviously a bit difficult here, because you haven't made an argument for it, but merely a statement, but again ultimately you would have to structure an argument based on it or it would be a pointless statement.
That was my point above. I cannot prove that Baha’u’llah was a Messenger of God and that is why I do not claim that He was a Messenger of God.
Again, I hope you see the difference in the above explanation, its not about your belief, but about what led to it. Those can be questioned and evaluated to figure out whether they are logically sound or rational.
Again, a person might say that they believe that Jesus were the son of God, but when asked how they reached that conclusion, they say that they did it, because the bible said so.
This is obviously not a sound argument for drawing such conclusion, because the bible is what made the claim in the first place. So clearly that is going to support that idea.
So I can't disprove your belief as such, but I can demonstrate from a logical and rational point of view, that your argument is not sound.