What I remember about ROOT Cint is that it was an absolute nightmare to work with, mostly because it couldn't do STL containers very well. It was a weird time to do language interop for physicists.
back in the days, one always had to have 2 terminals open to work with ROOT: one to work and the other to 'kill -9 root.exe' thanks to CINT happily completely destroying your TTY.
Modern ROOT of course replaces CINT with Cling and STL containers are well supported.