By International standards, and even by Australian standards, it's terrible. 60kph average for an "express" rail service. Anything under 100kph *average* is sub par..
Sydney isn't like other international places. This is what we have and we have to deal with it. Stop bringing up what international places are doing.
OK let's hop across to Perth which, last I heard, is in Australia. How would Transperth services run on this line if everything was up to scratch? Assuming Waterfall-Coledale was realigned, most of the rest of the line is pretty straight or gently curved like the Perth lines. Perth trains have a max speed of 130 km/h, Oscars 130, Endeavours 145 km/h.
Sydney-Thirroul vs Perth-Mandurah: both 70 km, with 5 intermediate stops on the NSW line and 10 intermediate stops on the Perth line. Sydney-Thirroul now takes 1hr 16min, Perth line takes 51 mins (**with 5 more stops**).
Thirroul-Kiama vs Leederville-Warnbro: both 50 km with 10 intermediate stops. Thirroul-Kiama now takes about 55 mins, Perth segment (which includes slowing down and winding through the city underground) takes 41 mins, not including 2 mins wait at Perth Station.
Kiama-Bomaderry vs Mandurah-Wellard: both about 30 km with 2 intermediate stops. Kiama-Bomaderry now takes 27 mins, Mandurah-Wellard 21 mins. (On the latter time they could turn the Endeavour around to run an hourly service instead of having to call in a bus.)
So, with a straightened line between Thirroul and Waterfall and whatever other touching up the line and signalling need, Transperth could run a Sydney-Bomaderry service in about 1hr 55 mins, plus changeover time at Kiama (which should be minimised on the present terrible gaps). That's about 40 mins faster than the present horrible south coast service, if you subtract the Kiama changeover.
Even without the work north of Thirroul, a service of Transperth quality could do the Bomaderry-Thirroul section about 20 mins faster (excluding the Kiama changeover time). That's something NSW Trains could try to accomplish right now without track realignment, but they just can't seem to manage it. Why not?