Larger gravel may be easier to clean from the standpoint of few small places to trap food, but the larger issue is there are too many places to store uneaten food, which then builds up.
In addition, the larger gravel is harder to lift with a gravel vac so you don't get that rolling turnover you see with smaller gravel. Also, with that gravel being large, more water is sucked into the tube and empties the tank before effective cleaning can be down, one of the issues the OP has stated.
I have cycled many tanks with fish food. And it didn't take a lot of "uneaten" food to start the chain and have nitrates through the roof.
Uneaten food from over feeding and expended food from the fish, whether it is useful to them or not will still rot and decay and add to the load of the tank. Countless people over the years have had tank crashes from disturbing substrate that held too much waste.
In addition, the larger gravel is harder to lift with a gravel vac so you don't get that rolling turnover you see with smaller gravel. Also, with that gravel being large, more water is sucked into the tube and empties the tank before effective cleaning can be down, one of the issues the OP has stated.
I have cycled many tanks with fish food. And it didn't take a lot of "uneaten" food to start the chain and have nitrates through the roof.
Uneaten food from over feeding and expended food from the fish, whether it is useful to them or not will still rot and decay and add to the load of the tank. Countless people over the years have had tank crashes from disturbing substrate that held too much waste.
