I'm not a doctor. I'm a former homemaker who spent years homeless.
But based on those stellar credentials, if I am understanding your question correctly, the answer is "both." It is both slower to access and also the reason you can wind up vitamin D toxic in a way that doesn't generally happen with water soluble vitamins.
You can get get too much of water soluble vitamins and they can do bad things to the body, but those bad things aren't described as "toxicity" because you don't build up excessive stores of them in the body like you can with fat soluble vitamins. Off the top of my head, some people who take way too much vitamin C end up harming their dental health by harming the tooth enamel and a certain B vitamin when taken in excess is associated with, iirc, kidney stones.
But based on those stellar credentials, if I am understanding your question correctly, the answer is "both." It is both slower to access and also the reason you can wind up vitamin D toxic in a way that doesn't generally happen with water soluble vitamins.
You can get get too much of water soluble vitamins and they can do bad things to the body, but those bad things aren't described as "toxicity" because you don't build up excessive stores of them in the body like you can with fat soluble vitamins. Off the top of my head, some people who take way too much vitamin C end up harming their dental health by harming the tooth enamel and a certain B vitamin when taken in excess is associated with, iirc, kidney stones.