"When there's a macroeconomic downturn, it's generally institutional and business lending exposures that are impacted first," he added.
For decades, Australian housing finance has significantly outpaced business lending, making home loan margins the engine of profits.
A more recent exodus from non-lending retail services like financial advice has further weighted banks' allocation of capital to residential property.
The big four banks said in earnings updates this month that their net interest margins peaked in late 2022 and have since narrowed.
To hedge against interest rates risks, the Big Four may now chase new services-based revenues from commercial clients in non-lending segments, added Garland.