louvers... Not my favorite although it seems to help the media from not tearing by (in my opinion) slowing down the oil flow.. Im sure that comment will bring some other beliefs..
Slowing down the oil flow through the louvers would INCREASE stress on the media, not decrease it. Although the whole thing is a moot point anyway.
A reduction of flow rate through a fixed opening means the flow rate through that opening has been decreased and 'slowed down'.
What a whole bunch of louvers does is help more evenly distribute the oil flow through the media. That in turn helps reduce concentrated areas of higher flow rate, which helps reduce the stress on the media in those locations.
If there were only two large holes in the center tube, then those two large holes would have to flow all the oil volume and it would also increase the stress on the media at those points because the flow volume per hole would be large. Evenly distributing all the flow through hundreds of smaller holes or louvers eliminates localized stress on the media due to concentrated high flow areas.