It’ll depend on which Vibram rubber compound they’ve used – some of their stuff like Megagrip and Idrogrip is very grippy wet and dry, other compounds more focussed on durability and less grippy, particularly in low temperatures. I’m guessing they’ve erred towards the latter.
I thought Salomon normally used their own Contragrip soles rather than Vibram and a lot of them are horribly slippy. To be pair, a mate of mine did the Spine Race in a pair of Speedcross and didn’t notice they were slippery on wet rock until I pointed it out to him.
I have also read lots of warrior reviews and no one moans about the sole.
Sometimes people don’t notice sole grip because they’ve not tried anything better, so they just see it as normal. You could get them resoled with a grippier compound if it bothers you. If you have a look at the Vibram web-site it runs through their different rubbers, but bear in mind that grippier with rubber generally means softer, which in turn means faster wear. Unless you add graphene as per the latest inov-8 shoes.