T3 begins at Liverpool while T2 starts from Leppington in which both stop almost at every station (after Glenfield: from Casula, Liverpool, Warwick Farm, Cabramatta, Canley Vale and so on, literally about 31 stations or so before you even reach Central). They skip Flemington, Homebush, Croydon, Summer Hill, Petersham, Lewisham, Stanmore or MacDonaldtown during peak hour at least, so there's that but the journey's quite long.
It takes like 65 minutes until you reach the city while the same Journey is quicker via T8. However the commute is still a slog to sit through as it takes forever and no other option if you live within areas of T2 (it's why T8 exists via the Airport and skips like 8 stations after Revesby heading for Wolli Creek) but it's only accessible for those living within the Campbelltown area. Don't even mention the commute time via T3, it's worse.
Both lines exist within the Sydney Trains network although are slow and long (well... people living in those areas don't really have an option, at least they have a station) with having to wait a while before they can even reach Central. T3 just heads via Regents Park then via Lidcombe intersecting with the existing T2 line to Central, regardless it's still takes forever due to the train stopping again, at every station on the way.
Either were the only option (alongside T1 via Parramatta) before T8 expansion via the Airport was constructed, and my parents who commuted during the 90s told me it sucks ass due to that stopping at 31 stations before reaching the city, when the Airport line finished construction: it was a godsend as it saved time on reaching the city circle deeming T2 or T3 a joke! T8 via Airport was only made because of the Olympics back in 2000.
Is there a question here ?