I do think that sorting is needed since transparencies are involved.
EE has 'Sort' function built-in based on quicksort.

As Esenthel said, billboards need to be sorted.

Y, i've seen myself the issue when i was trying to answer in the support, was wondering though if it's worth sorting them in a real scene and if it is noticeable from that distance, guess that as you said it is needed. Thanks for the answers.