I assume that any developer can buy a unit and then take the strata to NCAT and get an order that the defects must be fixed.
You assume correctly. So the predatorial developer finds a property with serious levies stress, buys one unit at a cut price, agitates for a major upgrade and maintenance program that requires special levies, scares the most indebted owners to sell at below-par prices until they own enough properties to prevent any other developer engaging in a collective sale while putting themselves in the box seat to do exactly that.
Strata law says common property must be maintained but the worst case I have heard of was a block where a cabal of owners pushed through a decision to dig a car park under the block then, when everyone else had sold out, cancelled the plan and ran the building to suit their own agenda.