Making Swordsmen not State Troops...
No, I think that the answer lies more in improving the Halberdiers as an option than in making any other troops type, Swordsmen, Knights or others, worse.
Improving the WS of Halberdiers certainly doesn't feel right; however, I believe that the Dogs of War list had a unit of WS4 Halberdiers, representing veteran troops.
Perhaps, then, it can come as an upgrade?
I can also see three other options.
(a) Swordsmen become Special Units. This represents their relative scarcity in the Imperial Army; then again, the Empire already suffers from too many good Special Units, so one more would probably be a bad idea.
(b) Decrease the points cost of Halberdiers. If Dark Elf Warriors can be 6 points, then Halberdiers can be 4. The two-point difference is enough to be noticed.
(c) Hit the points another way, and appeal to combat-resolutioners, by making the Halberdier command group free. On the battlefield this would lead to more Halberdier regiments, as well as nice Full Commands out at the head of more regiments. If combined with the above points cost drop, it could lead to Halberdiers returning to their prominence in the list in force.