PS: ISA (AS) is none other than Imam Mahdi himself. There is no need for Allah to send someone who he sent to people of Israel and Imam Mahdi who will not claim to be imam Mahdi AS.
Ah so now I see what point you are getting at. Fair enough if you think that is the case.
Now if we are going to present arguments for and against that one point...I am sure I can accommodate that. But then again we are not going to make claims and say "I THINK" and no claims like "PS: ISA (AS) is none other than Imam Mahdi himself." Saying two things are one and the same is like what Christians did at the Nicene meeting, i.e., trinity. But thats deviating from the topic.
So you are basing a theory simply on an assumption that Allah doesnt need two 'guiders' at the same time and claiming that Mahdi and Eisa (A.S.) is one and the same? Source for that claim?
I have already told you there has been many times when there was more than one prophet to the same area (geographic) at one time. So questioning why two are needed and then making them one is not a valid reasoning on your part.