This might depend what line you're on. If you were on the massive T1 loop before they split it, a few late trains were almost a certainty during peak hours. If you live at Bondi it's unlikely your trains will be late because the line is so short.
Don't get me wrong, I do think we complain a little too much about public transport in Sydney (when in reality, it's actually fine most of the time). But it definitely does have some pretty serious flaws (too many single points of failure is the most obvious one -- especially the Strathfield-Paramatta stretch of track which is core to the running of 7 [out of 9] different lines without any way to route around it).
Don't get me wrong, I do think we complain a little too much about public transport in Sydney (when in reality, it's actually fine most of the time). But it definitely does have some pretty serious flaws (too many single points of failure is the most obvious one -- especially the Strathfield-Paramatta stretch of track which is core to the running of 7 [out of 9] different lines without any way to route around it).