Compared to the rest of the world does SY handle the same amount of traffic as say O'Hare? (Planes per minute say) Could SY be utilised more if our ATC could handle it?
Whilst it against my nature to respond to obvious trolls; WTF? It's not exactly fair to compare an aerodrome with one parallel runway system with an aerodrome with three. Think of the TMA/TWR controllers at O'Hare and you'll find that SY is very competitive in terms of traffic to controller ratio.
LTOP is the primary factor determining movement rates; ie it is "capped" at 80 movements an hour. It is not the fault of ATC that LTOP exists and determines the rate (even if ignoramuses can't recognise that). You'll find that the Sydney TMA is configured in such a way that they are able to handle that rate or slightly more; because that is the hourly workload; to up the rates may have an impact on configuration, but then again maybe not.
The other considerations re movements are taxiways and runway exits and entries especially on the single runway mode; ie the strong Westerly wind days. On those days movements can be reduced significantly below LTOP caps to about 50 and hour; this is totally about aerodrome design and layout not the ability of ATC.