I got into doing IBM mainframe stuff by becoming certified by IBM as a DB2 DBA on AIX/HPUX/Solaris OS, i.e. IBM, HP & Sun *nix systems. The block mode operations on mainframes quickly drove me away. After decades of experience with interactive systems, block mode was a rude step backwards. Mind you my experience was with "traditional" IBM mainframe OS, e.g. MVS. I did dabble with Linux on 370's and it was a pain doing Unix commands using block-mode.

Mind you, all of the above was quite a few years ago. Things may have changed since.