I think your maths are way out. A single Y sale fare may go for $600 base, but they don't sell the whole lot at that rate - it is a mix, and the filed fares (for return) SYD-LHR state at around $1,600 - so $800 one way. I suspect the blended rate spread across those 341 seats is much closer to $1,000 per seat one way - so lets say $340,000
The premium cabin guestimate is even further out - and that is where the money gets made.
14 First - ranging from 9 ,000 to 15,000 one way - lets just say most are "cheap" at 10,000 average - so there is $140,000
70 Business - ranging from $4,500 to around $11,000 one way - average likely to be around $6,000 plus - so there is $420,000
60 PE - ranging from $2,400 to $4,000 - keep it low and just work with $2,500 - so there is $150,000
This is equally rough, but gives a total (admittedly for full load), more like $1,050,000 - of which two thirds or so comes from Premium cabins. That sort of ball park sits much more in alignment with
@Himeno reported figure for the Woolworths trip (albeit that was US not UK).