You're right about everything. But I'd argue if we're going to dedicate time to 'guys', we should no less have a meeting about every single other possible ambiguity that hardly matters, and try to somehow encourage inconvenient changes to people's natural vocabularies.

Similarly to the article above, during the meeting, no alternative was suggested. I like the word 'guys' for its casualness. If you're at risk of being perceived as somewhat authoritative, it can help induce a more casual tone. I thought about 'peeps' but that's too casual (and frankly weird, in a business setting). 'Everyone' is far too sterile. 'Ladies and gentlemen' is weird. 'All' (e.g. 'hi all') is also impersonal.

Workplaces could over-analyse and pick about minutiae all day long, and how productive is that? I reasoned that if we are going to pick about minutiae, then it should at least be the worst of the worst offences, and should be accompanied with some alternatives or solutions. Not just "Don't do <x> because I said so" type of thing.