Wouldn't these be RPT with a known schedule.
And there are still many variables; using SY example, BTH, CB, NWA, WLM, ORG etc (will have known RPTs at times), but as you know they don't get away on time every time, some operators in the past didn't follow their departure times at all accurately. Pretty easy to get a 30 sec to 3 minute delay (or the delay removed because the CB jet didn't go on time) from somewhere to back up against an otherwise perfect sequence... Which means the whole thing is going wrong somewhere... Pigeon/Statue?
Then there are those pesky issues, such as a go-around, a medical flight, an emergency, an extra space due to taxiway congestion in an effort to get a few more airborne, weather (changing winds not scheduled, low vis etc.), a blocked frequency, unknown operational speed issue, etc. etc. If it were as simple as one follow the other etc then ATC would've been automated a long time ago.
I have also experienced FF (feeder fix) times given with 200+ miles to go getting completely bolloxed up... where speeds and vectors were needed to make it work... etc... Modern boeings seem to be more accurate, but there are also "how to get there on time" issues, go normal in cruise slow in descent vs go slow in cruise and normal on descent etc... It's not as simple as giving times and forgetting if the aircraft are a dead heat 80-120 before the fix...
In enroute we used to say "nail the first, stream the rest"... Which is easy when it's your stream, but if APP/DIR are merging arrivals alternatively from North East and West then what happens coming through RIVET etc is totally irrelevant if if the ones coming from the other ends aren't where they should be etc... I'm sure you'd rather comply with speeding/up/down as needed too to keep SY at 80 movements an hour rather than 75 etc... because everyone knows an airport not working at capacity isn't working... (let's not discuss political movement caps...)
PS you could fix almost everything if you went the European way and accepted delays in the holding stacks and on gates or airfield parking bays and forgot all about slowing down enroute, except for separation... I think the Australian way is much more 'efficient' even if pilots don't think so. Pilots don't seem to complain over here maybe because it's busier??? The reality it isn't, the busy bits are no busier they just last longer.