Asalamu Alykum
I think this is a tough question to answer.
Only God really knows the intention of people and how they are associating past prophets, messengers, pious men, angels, etc to God.
I don't think believers should be condemning such writings and claiming that such proclamations are going to cause one to be a disbeliever or that it is not allowed as we can't verify what the intention is behind it and the fact that it can be qualified by the Quran by different verses combined. I think we should be more cautious as we may be calling someone a disbeliever and they are not.
Read the article below and there does seem to be a suggestion in my opinion that
"if" the shahada as we hear it today was established by believers in the time of prophet Muhammad(pbuh) they were possibly aware that they are just witnessing that the prophet is true(3:86).
Also the article makes a good point by this statement "
However, it is also to be appreciated that the above testimonies were 'qualified'. Rather than asserting the belief in any 'One God', God was qualified as the God of Solomon, Moses, Aaron (pbut) or the Children of Israel.
"
So I would say that for a person who now knows the differences should make clear to at least theirselves and of course the Lord that he/she believes in One God and there is no other than Him, which is the God of the prophets and messengers who were part of the religion of Islam.
So from the other testimonies that we hear we really don't know what one really intends by that. However the mainstream shahada can be qualified as true from the Quran.
Also again maybe the first believers thought it was important for them to distinguish between the belief in any One God with the One True God of Moses, Jesus, Abraham, Muhammad and all the prophets and messengers under the religion of Islam. God knows best.
Also just as important there is no warrant for those to say that the main stream shahada is the only testimony accepted by God as the actual shahada taught by the Quran is "There is no Diety except Him (God)" meaning the One True God who is the Creator of everything.
God knows best
Peace