The breaking of cross terminology found in Ahadith is in context of return of Jesus (AS). Traditional view is that those prophecies relate to physical return of Jesus (AS) while Ahmadi viewpoint is that they were prophesying about return of a Messiah just like Jesus (AS) because Jesus (AS) has actually died and is not going to return as believed by traditional scholars.
Ghamidi Sahab also believes that there are few passages in the Quran which do indicate that Jesus (AS) has passed away (some very explicitly state this fact), therefore, all such narrations related to return of Jesus (AS) / Messiah when seen in the light of Quran, become dubious. You can read his views on Jesus (AS) and Imam Mahd in the following thread (starts right after10th point mentioned in the article):
Discussion 30985
Secondly, the reason for end of Prophethood has had bigger reasons and implications at a philosophical and practical level than just breaking of a cross. For opinion of Ghamidi Sahab why Prophethood came to an end and how does claim of Prophethood actually compromises Quran’s authority as Meezan and Furqan, please refer to following threads:
Discussion 3442
Discussion 4209
For complete elaborated thread on Finality of Prophethood, you can refer to the following thread:
Discussion 4625