The word "beginning" in Rev 3:14 is translated from the Greek word, archē.

The definition of archē according to Strong's is:
"a commencement, or (concrete) chief (in various applications of order, time, place or rank): - beginning, corner, (at the, the) first (estate), magistrate, power, principality, principle, rule."

And according to www.greek-dictionary.net:
"beginning, origin, first; ruler, power, authority; position of authority, domain."

Rev 3:14 in no way supports the Unitarian idea that the Son of God is a created being. And there is no such verse in the entire Bible which proves Jesus is a creature. Yet there is an abundance which proves Jesus has no beginning.

Read Colossians 1:16.

" For by Him [Jesus] all things were created, both in the heavens and on earth, visible and invisible, whether thrones or dominions or rulers or authorities—all things have been created through Him and for Him. " (Col 1:16, NASB)

The Creator of all things cannot be a created thing. That is just simple logic.