There are lots of languages where the gender-neutral term and one of the gendered terms are the same. Consider the Spanish "ellos", meaning either "the masculine group" or "the masculine and feminine group". The word "ellas" denotes a feminine-only group.

It seems very reasonable that "guys" could function similarly in English. Moreover, I might not say "the guys I've dated" as a straight man, but if all the women I've ever dated were talking together in a room, I wouldn't bat an eye asking "what are you guys all doing?".

Similarly, I wouldn't say "all the folks I've dated", but I might say "good evening, folks" -- the word is a misfit solely because of the idioms and context, not because the word is inherently communicating something else.

"Guys" tends to be neuter in the second person and masculine in the third person.

In any case, I think your example works better with a bisexual speaker. A straight guy would probably use more specific gendered language rather than a neuter construction. A bisexual person using "guys" to refer to the men and women (s)he has dated would be an example of a third person neuter usage—which I also think would be quite rare.

A nuance of that usage of "guys" to refer to a group consisting of both men and women is that the group of people being referred to is typically immediately present in some way.

Like in those earlier examples, the people are probably all within the same house/yard at the same time when they're called to dinner, or they're all using the same online discussion forum at about the same time.

When discussing multiple individuals with significant time and/or distance separating them (like the people somebody has dated over the span of years), a more specific term like "men", "women", "men and women", or "people" would likely be used instead.

Here's a shocking concept: language has context.

Glad it's not up to you to "buy" the words I choose!

My region uses "you guys" for the you plural in English, too, and you petty speech totalitarians didn't show up until I was grown so even though I now live in a region that says y'all and even prefer it, when speaking I form sentences in my native language too quickly to catch myself every time I use my native term for you plural

But you and your language policing petty authoritarians would have me sent to the gulag for your ridiculous overly academic context ignoring willful and politically motivated misinterpretation of my diction

Screw you!

I haven’t used “guys” in that specific way, but I’ve definitely called my various female partners “dude” before. Language is fluid etc.

I don't think this example counters the gender neutrality of "guys". Have you ever observed a straight man talk about the people he's dated?

Why would they use it to refer to a group of exclusively women? 'guys' refers to a group of men or a group of men and women, not to a group of women. Is that so hard to understand?