Looking at all this, it seems that their batting performance is currently deteriorating, but I will say here that in the case of all teams, sometimes good performance continues, here we also see a drop in performance sometimes.
And this is probably what is happening with the Australian team right now, I would say, they are facing this in the ODI format.
Australia is still the best team and probably on the same level as India, and bad day can happen to any team and they can even crumble under 100 for team total but it should not be considered as their actual potential, they can play better than that.
I am not watching any of these SA vs AUS tour but it could be due to the fact it's just a bilateral so they didn't go with their full potential because if we look at their history they will look like an average team until the day comes like semi or final then they will play like no one can beat them. Travis Head was overhyped due to the IPL so he should recover from that and focus on his batting, apart from that everything is good in Australian team.