I was just thinking that you are ok with a divinely selected leader called Mehdi who is not a Prophet, so what shall we call him....hmmm what is arabic for leader.....Imam.....but then you don't believe in divinely selected Imams......
Hmmm....
firstly if we have one divinely selected leader at end of times why shud he be preceeded by 11 ( and mind you only 11) others ?
why shud there be a break of 1400 yrs and who know how long until imam in gahybah appears ?
word imam though commonly associatted with 12ers is by no means unique to them
u can take and play with this logic as much as u want .....but we only have hadith and history to consult and in light of this we can come up with the best conclusion and God knows best