Wa alaykum salaam
Thank you for your question. There is no problem in naming a child Mahdi, Sadiq, Kazim, Haydar, Sajjad or any other epithets of the Imams (as) commonly used for naming children. Indeed it is cited in hadith that one of the responsibilities of the father is to select good names for his children and some of the best names are the names of the Infallibles (as) and their (as) epithets. Special stress has been placed in our hadith on naming a child Muhammad or Fatima and there is also a responsibility attached to naming a child with these two names.
The reasons given in your question for not naming a child Mahdi have no basis.
May you always be guided and of the companions of al-Mahdi!