John 17:5 and EINAI

There is a YT channel known as TheTrinityDelusion. The owner had made a video on John 17:5:

https://www.youtube.com/watch?v=31-BQt-7_5c&feature=youtu.be

I believe that he errs by not being aware of how the Greek infinitive EINAI is sometimes used idiomatically or in certain settings. The rendering "was" is perfectly fine for John 17:5; more specifically, as A.T. Robertson writes, we should understand the passage to be saying: "'before the world was' (pro tou ton kosmon einai), 'before the being as to the world' (cf. verse John 24)."

I'm also including a link to Lesley Brown's article on EINAI in Greek philosophy.

See http://www.philosophy.ox.ac.uk/__data/assets/pdf_file/0005/16673/The_verb.pdf

See also https://books.google.com/books/about/Toward_a_descriptive_analysis_of_einai_r.html?id=s2UXAQAAIAAJ

http://www.jstor.org/stable/3265495?seq=1#page_scan_tab_contents