I have a hard time believing the Venturi effect has any measurable impact in an oil filter, considering that the entire thing is at the same pressure, and there are hundreds of louvers to allow plenty of flow.
Everything I’ve seen about louvers was strictly a cost-savings measure; louvers do not create millions of little steel circles to errantly end up in the filter or be disposed of. Simply punching a slit is more efficient than stamping a hole. Same thing with plastic cages; there’s already plenty of flow, but plastic cages are cheaper than steel tubes regardless if it’s holed or louvered.
I’m from Missouri here- show me a documented test that shows louvers increase velocity thru the media, please. 👍🏻