Totally agree, three slots would be better. Every player having a potential choice of three weapons and a shield or to weapons and two shields leads to most of the players becoming fairly general. It would be more interesting if people had to specialize more and it mite even encourage teamwork a bit. This would have to include the idea of the bundling of arrows/bolts with bows and crossbows though.
As an even more extreme idea you could have the slots divided up into weapon types. For example you could have one main weapon slot allowing any weapon, one secondary slot only allowing smaller 1h weapons, and one shield slot. And of course grate long axes would take up all three slots
Edit: This would solely be for the multiplayer of course. In the singleplayer its being able to be so generalized that makes battle so interesting.