The fares quoted are one way, I can easily find return tickets for half of those prices. Booking a year in advance is a bit too much, around three months ahead will get a better deal. Premium economy is nearly twice the economy fare and for a flight of around eight hours, difficult to justify. Also P/E fares on a direct route with a major airline get quite close to business class fares on a second level airline involving a connecting flight.
The London - New York route is weighed towards premium passengers who keep the price down in the rear cabin. A business class ticket is typically 5X the economy fare, where as London - Bangkok is around 3X.
Someone wanting LON - SYD without a stopover on the way might be able to justify the extra expense as they will be onboard for nearly 24 hours with only a short refuelling stop to break the journey and will need to get a few hours sleep.
An Auckland - London flight via Los Angeles or Singapore would be one of the few routes where business class could be worth paying for.