Sounds like you’ve never tried to use it. Unreliable and slow. Over the past few days it’s been a 5 hour bus trip.
What we should really complain about is how we've not had the foresight to build and open true high speed rail linking our two major cities, and importantly, serving those who live in wonderful locales like Albury or Wodonga. I hear your frustration, because many other nations have built this and that technology keeps on improving. It would be terrific, but we lack decision makers at all levels who can learn from what other countries do.
Sorry, but I've used it more times whether Melbourne to Sydney or intermediate stopping stations than one could poke a stick at, day and night, just as I've been by both train and car to Albury/Wodonga numerous times over many years. I also used the former three intercapital trains, long since ceased.
Some recent days IIRC have seen some scheduled trackwork. This isn't often, but like airfield runways - LAX is one to which you used to refer, and soon MEL when it starts its third runway construction - there's work that cannot fit in between trains, even though the line is duplicated between Seymour and Wodonga, and in part closer to Melbourne. There was one instance where due to works being incomplete, a train took six hours from Albury to Southern Cross I gather - unacceptable.
Provided the trackwork isn't for weeks on end, it's unfair to criticise this, unless you'd prefer a train to derail, or to have to crawl over mudholes for ever, instead of them receiving attention from the Australian Rail Track Corporation. Ideally, there shouldn't have been mudholes when the westbound track was gauge converted several years ago, but that's history.
If you're referring to the NSW XPTs, they're not that slow. Average speed of c.85 - 90kmh Melbourne to Sydney that considering the railway north of Junee to Sydney is curvaceous, being built in the steam era, is creditable. Of course, nowhere near modern high speed rail median speeds.
Between Southern Cross and Albury, with four intermediate stops, the XPTs are timed to take 3 hours 15 to 3 hours 22 minutes. It's 315km by standard gauge rail via Sunshine, so average speed of as fast as 88.8kmh. Trains can't stop from a speed of 120kmh in 130 metres like many cars could, so the stops (with a typical minute plus at stations as well) slow it down.
When V/Line and NSW TrainLink have replacement road coaches, which I've travelled on quite a few times including in the past year, they usually take about 3.5 hours from Albury to Southern Cross, subject to traffic close to Melbourne - the express ones. For roadside passengers, stopping buses take longer, but the XPT only stops at Broadmeadows, Seymour, Benalla and Wangaratta (whereas V/Line has a few more stops: Avenel, Euroa, Violet Town, Springhurst and Chiltern, plus that large city of Wodonga.) V/Line always has an 'express' coach in such circumstances (that usually runs Southern Cross to Wodonga then Albury or vice versa.
It's usually irregular or non-users (you?) who claim the XPTs are unreliable. In summer, these trains, as with V/Line's can run late due to 90kmh heat speed restrictions imposed between IIRC 1200 'high noon' to 2000 or 2200 hours if the temperature is forecast to hit 36 or above. In practice if the BOM overestimates the temperature, they can occasionally be lifted, but they are a pain for travellers and not ideal, though some other railways worldwide also impose these.
The rest of the year, pretty good considering these trains are around 35 years old. As a lady recently said to me in one of the cities along the route 'I like the XPT: it's a pleasant journey', which it is, especially in first class.
Tonight's Melbourne - Sydney XPT is presently 34 minutes late while the southbound ex Sydney is two minutes late. That's better than Regional Express' performance ABX to MEL on many days (or for that matter when there's fog or other problems, ZL, QF or VARA from ABX to SYD.