ARAM is random so you just have to pick whatever you best at of the 3 you get. Mirror matches are within the rules of ARAM so if you dont like it then just leave like everyone els does or try and play it.
Then it would not be ARAM any longer if you want a 100% garanti tank or healer to pick. Its random for a reason.
Trolls would just spam that button until you do what they say. Surrender was never added cause devs said we dont need it. Games are not that long that you need it and adding a surrender would just make the game more toxic.