One problem I have with libedit is that it (to my fingers) doesn't seem to work as well as readline. I was also part of this thread, not because I had problems with multibyte characters, but because I *definitely* noticed that things that used to work weren't working anymore.
tl;dr: my unexpert opinion is that libedit is not as good, or psql is not very good at using it, and it makes my hands angry.