Not sure, Gar. Kentucky bluegrass is tight--but perennial ryegrass does not knit together as well. A lot depends on the cultivar or variety of Kentucky bluegrass. The athletic types that are often used on baseball fields and golf courses will be suited to a shorter cut, yet remain dense if cut often, with quality, sharp equipment.
So sorry, it must be difficult to control weeds and keep lawns looking good without herbicides. A lot depends on what height-of-cut discourages what weeds. And what fertility level discourages what weeds. Dandelions grow low, likewise veronica. I think oxalis, violets and clover might be discouraged by short mowing. What is your experience? Are you hand digging dandelions?
Are customers accepting of a few weeds now that herbicides have been outlawed in Canada?
I used to have a couple of earth-conscious customers. One got 10 minutes of hand weeding at every fertilizer application. The second got Quicksilver treatments--because the toxicity is so low, and only a few drops per thousand sqft are needed. Also I agreed to spot spray, because spot spraying uses about a hundred times less chemical.