I've ridden through torrential rain for hours, and nothing has ever got wet inside my cotton duck Carradice. I used to have Overlanders, which were nylon, and gave in to rain after an hour or two, so it was worth lining them.
I use a Super C saddlebag every day, as well as panniers front or back, wedge pack, and barbag. My partner has a Camper longflap and a Barley, and I also have a Barley. Oh - and my son has a Junior. No rain problems, even when the bar bag has a pond on the lid.
I don't like Ortliebs partly because they're a faff to get in & out of. I much prefer a fastex buckle. The other reason is that I like to keep things organised and handy by using pockets. Ortliebs don't have them as standard and, while you can fit them (at great expense) afterwards, it compromises the water resistance.