A high water flow rate increases gas exchange - CO2 out, oxygen (O2) in.
Biological filtration capacity is often limited by lack of oxygen, not lack of filter material, bigger is only better if sufficient oxygen is reaching all the of the aerobic bacteria in the filter.
A large capacity wet/dry trickle filter, where the thin film of slow flowing water will become fully oxygenated, is likely to produce much more highly oxygenated water than most other types of filter. A back up for both biological filtration and aeration is essential, battery powered air pumps and sponge filters can be the difference between life and death.
To fully utilise the filtration capacity of a large volume canister filter, water flow, and the oxygenation levels of that water, must remain high.
Bulky organic debris (food, faeces, saw-dust) can reduce the filter capacity for nitrification and aeration, both by the oxygen consumed during decomposition, and by reducing the flow speed, and water volume, passing through the filter.
Plants and substrate can contribute to maintaining water quality, and therefore oxygenation.
Aeration, using an air pump and diffuser, can increase oxygenation,but only if the bubbles are very fine, and have a long “residence time” in the water column or filter.