Peak Design Everyday 6L
Peak Design
$130 / lifetime

Weather resistant indeed after walking through a steady rain for 3+ hours. A bit smaller on the storage factor than you may like, but the light and small footprint of the sling makes up for it (alongside the easy-to-use straps for adding a tripod, jacket, etc. to the bottom of it).
It stores a surprising amount via the front zipper area, the interior zipper area, and then the main compartment itself. Reorganizing the dividers is always good when needed, but mostly for being able to safely, snugly carry my camera gear around.
And I'd strongly recommend this over the 3L, which isn't a much smaller footprint but it is much harder to open and stuff things into than this, where the zipper goes much lower making it easier to really pull it apart and pick things out.
I've also taken to stuffing packable tote in there as well, so if I end up buying some junk and need extra carry capacity then I simply unfurl that bad boy and voila, I've got it covered (and zipped, and also waterproof, etc).
A lifetime warranty again from the solid customer service folks at Peak Design.
¶