I think you describe the fact that the B777's fly via the Richmond SID (turn @ 1500ft), out to 12NM from YSSY then turn towards track.
The 744's and A380 would fly the Sydney Radar Departure, which is normally runway heading then a turn subject to traffic.
A driver will be able to confirm, but the 747, close to MTOW can't achieve the climb gradient required for the RIC SID, thus they fly the SYD 1 SID.
The turn towards RIC is due to noise but also brings into the fray more obstacles on the track which requires a greater rate of climb. Something which the 747/A380 evidently is unable to do.
Happy to corrected!
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