The allegation is that Ahmad(as) has claimed to be all of the prophets. This is totally incorrect. Ahmad(as) has only claimed to have the qualities of all of the prophets and this is completely true. He did indeed have the qualities of all of the prophets.
There is an ayah of the Qur’an which also metaphorically hints to the latter day messiah having qualities of all of the prophets. Allah states:
And when the Messengers are made to appear at the appointed time —(Chapter 77 Verse 12)
“It is written in Barahin-e-Ahmadiyyah that Allah has made me a manifestation of all the past prophets (peace be upon them) and the names of all the past prophets have been attributed to me. I am Adam, I am Seth, I am Noah, I am Abraham, I am Isaac, I am Ishmael, I am Jacob, I am Joseph, I am Moses, I am David I am Jesus and I am the complete manifestation of the name of Prophet Muhammad (sa); that is, as a reflection, I am Muhammad and Ahmad.”(Haqiqatul Wahi Page 76)
He also stated:
“This revelation means that I have been bestowed some portion of the special circumstances or special qualities of all the prophets, peace be on them, who have appeared from God beginning with Adam till the end, whether they were Israelis by descent or non-Israelis. There has not been single prophet of whose qualities or circumstances I have not been bestowed a portion … In this there is an indication that many people of this age resemble the bitter enemies and opponents of the prophets, peace be on them, who had exceeded the limits in their rancor and who were destroyed by various types of torments … There has also been displayed and will be displayed in the future the various types of aid and support which God Almighty had displayed in the case of the previous prophets.”(Braheen Ahmadiyya, Part V, p. 89)
Many saints have said similar. For example Sheikh Abdul Qadir Jilani(ra) has said :
“A person rises till he arrives at a station where he becomes the heir of every messenger, prophet, and siddique”(Futuhul Ghaib, Maqalah page 23)
Hazrat Abu Yazid Bastami(ra) has stated:
“What is the ‘Arsh or Throne of Allah?” He
responded, “I am.” It was asked, “What is the Lauh and Qalam?” He responded, “I am.” It was asked, “It is said that Abraham, Moses and Muhammad (sa) were righteous servants of God?” He responded, “I am.”(Tadhkiratul-Auliya, By Hadrat Shaikh Fariduddin Attar, Chapter 14, p. 128)
Another famous saying of Imam Baqar(rh) is as follows:
“The Imam Mahdi will say: ‘O ye people, if any of you wishes to behold Ibrahim and Ishmael, then let him note that I am Ibrahim and Ishmael. If any of you desires to behold Moses and Joshua, then let him note that I am Moses and Joshua. If any of you desires to see Isa and Simon, then let him note I am Isa and Simon. If any of you desires to behold Hazrat Muhammad Mustafa, peace and blessings of Allah be on him, and Ameerul Momineen Ali, may Allah be pleased with him, then let him note that I am Muhammad Mustafa, peace and blessings of Allah be on him, and Ameerul Momineen Ali, may Allah be pleased with him.”(Baharul Anwar, Vol. XIII, p. 209)
It is clear that the Imam Mahdi would make this claim, and would have the qualities of all of the prophets.