It is very reasonable if you are a Baha'i who believes in
Bahá’u’lláh and His Covenant.
Otherwise I would not expect anyone to consider it reasonable.
Baha'is are supposed to personally investigate the truth. How thorough do most of them do that? Since they can never know everything, then as time goes by they learn new information. Since many people do dropout of the Baha'i Faith, what happened? Did they find out that it wasn't to their liking? Maybe some teaching or maybe the actual practicing of the Baha'i Faith wasn't working for them?
Again, I compare it to born again Christianity. How far will a person keep believing what they are being taught? Jesus loves them and died for them? Without Jesus they will go to hell. Satan is real and trying to put doubts in their mind. Jesus rose from the dead. People came out of their graves in Jerusalem. Then add the rest of the Bible. Jonah survived three days in the belly of a big fish. Daniel's friends survived being cast into a furnace. Moses' staff turned into a snake. The seas parted for the Hebrews. God created the world in six days and so on.
There is great spiritual power in believing and knowing the truth. But every religion and every sect of every religion has a slightly different version of the truth, or even a very different version of the truth. They feel that power. Like I've said before, the only constant is that the person believes their religion is the truth. They all can't be right, but they all think they're right. Lots of us throw out questions to the Baha'is, and the Baha'is always come back sounding just like those "true believing" Christians, they "know" what they believe is the truth. No matter what Baha'u'llah or Abdul Baha' says, it is the truth because they are infallible.
All Baha'is have done is add one more unprovable religion to the mix. If it works for you great. But in "knowing" your religion is true, Baha'is have to tell everybody else in every other religion how wrong they are. For me, there is no "progression" of religious truth where the spiritual laws stay the same and only the social laws change. Even spiritual truth has changed. Ideas about the Gods and God and no God have changed. Where people go after they die has changed. To me, it's almost like people are making it up as the go along. Which kind of makes it seem like a progression. But not like the Baha'i concept of progressive revelation.
Do Baha'is have God's laws that are necessary for this age? Then how are they going to implement them if all or at least the majority of people don't join and believe Baha'u'llah is the Christ returned? So let's suppose that Baha'is do become the majority. Are you going to tell me that in the future the LSA, or at that time, the Local House of Justice, a body of elected Baha'is from the community are going to know how to run a city government? How is that supposed to work?