The mission workshop bags have 100% waterproof compartments. Your dakine claims to have "rain resistant construction" For example you have soaked dirty clothes, you can put them in a compartment and it won't effect the rest of the bag. And rain is not getting in as the compatments are all zippered. The vandal has 3 waterpr oof compartments.

Your dakine is 1600 cu in. The vandal is 1800 cu in and expands out to 4000 cu in. Over twice as large and normally carrying a bag no bigger than yours. It also has independent load adjustment straps. These bags are for carrying serious stuff. That elastic strap can be used to secure things to the outside of the bag. There is a video on youtube of a guy carrying a full bike in one of these bags.

Not sure why you would need a waterbottle holder in your bag. Put it on your bike or in your bag or attach it to the outside.

They also look nice. Nice stuff costs money. There is no comparison between a $40 bag and a $250 bag.