BG has said in interviews that the Embraers are better for routes that are at least one and a half hours or two hours long. That hardly makes the Embraers a wrong decision. No jet is better than a TP on a short stage like SYD-CBR. Of course DJ could go back to the bad old days of cross subsidising Canberra flights from profits made on other routes, but they would need a protected Two Airline Agreement to make that work.
Depending on cost of fuel, some people say a jet starts to win on routes of longer than 350 miles, so the Embraers would be better choices for BNE to Mackay and Rocky than Q400s. Are the slots available at SYD if DJ wants to match the frequency that Qantas offers between SYD and CBR with TPs?