Define "guy"

Yes, it is a now a very general informal term for companions.

Informal ... so its substandard ?

No, there is nothing substandard about informal English-- it is merely English we would not use in a formal situation-- speech, essay, etc.

You are correct, non-professional English is somewhat "sub-standard" and should NOT be used in a business setting. We don't use the term sub-standard as much as inappropriate. As a woman, I hate being called "you guys" and I know other women do, too. It is not acceptable to call an executive or someone above you in an organization "guys" and it is in appropriate.

I am a woman and I can't stand being referred to as a "guy". The English language is full of acceptable contractions, such as isn't, can't, wouldn't; you get the idea. What is so wrong about referring to a group of males and females as "you all", or contracted to "Y'all". I see no difference in that or any other contraction. I find it much more preferable and appropriate than addressing a group