I don't think we need to overtly focus on building every type of ship during a war. I'm not sure the war will be long enough. I'm not sure we could train the crew fast enough even if it was years.
But maintaining ships, repairing ships, yes. Building drone ships, building drone aircraft. Yes.
Replacing major fleet vessels and manned ships during even WW2 was a big hassle and ask. Which is why you need to have what you need to have before the conflict. Even for the US building major surface combatants during a war was a major endeavor. We can't expect that we will have 10-20 years lead time, then use that time to build the fleet we need for war. We need the major fleet units to be there ready to go, crew trained.. You can't just conscript a fleet of sailors anymore to man modern surface combatants and submarines.
The reason why we built corvettes isn't because that was the best ship type, it was because that is what we could build.
As for why to build in Australia. Look around. How confident are we on our American built subs arriving? If you don't build it here, it may never arrive. Even with the best yards and the best of alliances and for all the right strategic reasons, there is, doubt.
We don't want to play the high attrition manned platform game. We will lose that, and lose badly. We could certainly do what ukraine is making, and make drones. Sea and air. They aren't making destroyers and Fighter jets. Although previously, they did during peacetime.
TBH im not sure anyone will be able to make anything during a global war. Chances are shipyards will likely be continuously targeted by drones. I'm not sure you can expect that for 12 months nothing is going to happen to a shipyard and that it will operate at better than peacetime capacity.. Shipyards are notoriously unmovable, big, close to the oceans and seas, and often contain flammable items, like welding gas, paint, oils, fuels, etc.