Yes, but under the large majority of circumstances, you will go OTB long before your front wheel locks. On slippery surfaces, like ice and snow or mud or sand, a front wheel skid is a concern. On dry surfaces, it just doesn't happen. Using only front panniers. In fact, the additional weight on the front wheel will provide greater traction - it is actually harder to lock your front wheel with loaded front panniers. The front brake is not rendered any more effective by weight on the front wheel. In fact, it becomes less effective, as it would no matter where extra mass was added to the bicycle. Oddly enough, putting weight on the back of the bike would make it easier to lock the front wheel, as it would add to the resistance keeping the back of the bike on the ground. I don't see this as any particular advantage, partly because I think it would make little or no difference in maximum braking performance, and partly because it would take a fair amount of weight to manage, but you can have it if you like.