Gals comes across as even more old fashioned than actress in my region - it's a term that feels like it walked out of a movie old enough that it had to advertise that it had colour.
Sometimes, as the world evolves, gendered terms get replaced by new gender neutral terms. Sometimes the meaning evolves in different ways (e.g. doctor and nurse are no longer gendered equivalents of each other, as the division in roles has continued to be useful even after the gender stereotypes as to who does those roles slowly fades). And sometimes one term just subsumes the other.
And sometimes, these changes happened many decades ago in other countries that are not yours. It's not very inclusive to expect those people to defer to American expectations of those terms.
The phrase "you guys" is attempting to be evolved, by parties who use it currently, and don't want to change their behavior to be explicitly inclusive. I'm not going to speak to what's okay in other countries, but the English definition of Guys is from Guy Fawkes, and is intended to mean a man. I would be surprised if the etymology of that weren't the same for Australia, which was also a British colony.
But the last thing I will point out, is that it's not on the in-group "men" to say whether or not they're excluding people. It's the people who are being excluded who get to make that determination for whether or not they feel like there are barriers for them. So when men say "you guys" is inclusive, they're saying "I don't want to change my behavior, so this now includes everyone." And the thing that's being ignored is that there are people who don't agree that they are included in that phrase.
Most of the replacements you cited are regional:
- Y'all is Southern/AAVE.
- Them is third-person, whereas "you guys" is second-person.
- "Yinz" is from Pittsburgh.
- I'm gonna throw in "youse," one of my faves, which is from New Jersey/Philly.
"Guys" is clearly gendered, whereas "you guys," I'd argue, generally isn't--especially in the Northeast US. I frequently hear cis women refer to groups of entirely cis women as "you guys."
This isn't meant as a view of what the ideal state of the English language is (bring back "thou!"), but these discussions frequently involve people talking past each other, and conflating "you guys" (second-person plural, arguably gendered) with "guys" (third-person plural, usually gendered). Effectively replacing "you guys" is a more challenging task, since there isn't a universally agreed-upon alternative, at least in the US.
I'll leave it to others to figure out what that alternative should be, though I will note that I, as a WASP from the Northeast, sound completely ridiculous saying "y'all."
The recognition that "Guys" is gendered, means that "you guys" will read as gendered to people. And that it will be necessarily exclusionary if you don't identify that way. It's worth noting that "you" is gender neutral and plural on its own. So it's hard for me to accept that adding a gendered word to a non-gendered one magically takes away the gendering. Also, the only people I ever see complaining about having to change this are people who fall into the group that's definitely included in "you guys".
Me <- WASP from Northwest that adopted y'all later in life, because it's just fun to say, and completely unambiguous.
"There is not always a counterpart", means that you recognize there is (at least) sometimes a counterpart. And in English, (unlike say, French or Spanish), the fact that so few words are gendered means that it's actually relevant when they are. Guys is masculine, Gals is feminine.
There are actually unambiguously non-gendered plurals "y'all", "them", "yins". Some of these are colloquial, but their existence also points to the fact that there are groups that weren't served exlusively with the gendered "guys".