The biggest problem I saw with the original SFS was simply its size. The concept was great, a rectangle specific stadium that would be better for league, union and soccer than the SCG was. Problem was that for Australia's largest city it was too bloody small. When it opened it only had a capacity of 40,000 which was 10,000 less than the SCG that it effectively replaced. In a city that is effectively dominated by rectangle pitch sports, it was just too small.
At the time it should have been built with a 60,000 capacity (IMO). Although as it turned out, even though they added another 5,500 to the capacity over time even that was too much, especially given at the time they already had ANZ Stadium which held almost twice as many. They rarely even got close to filling it for anything other than high profile union tests or soccer internationals, or for Origin's and Grand Finals. For club football it proved too big most times for the Chooks, Waratah's and Sydney FC. Yet they are rebuilding it in practically the same configuration and capacity.
Tearing the old one down and building one basically the same other than being 30 years more modern doesn't make any sense. For mine now it shouldn't be any bigger than 30 or at best 35,000. Its not going to usurp ANZ, especially when that place is re-configured so to me it just doesn't make sense to build it as big as they are going to. Something more along the lines of what they did with bankwest would have been a much better choice.