Looking at all the other options out there, I agree.
Comparism:
swordsmen have I 4, WS 4, Sv 4+ (CC)/ 5+ missle fire, S 3
spearmen have WS 3. I 3, Sv 5+, S 3, effective two ranks attack
halberdiers would then have WS 3, I 3, Sv 5+, S 4.
In effect, improving the survivability of halberdiers makes them a lot more viable as a unit. If survivability goes up to the same level as spearmen, you get to choose between better CC survivability (Swordsmen), more CC attacks (spearmen) or higher strength in CC (halberdiers).
In my opinion, bringing halberdier survivability up to par with the spearmen should vastly improve their usefulness. Unlike WS 4, which IMHO doesn't cut it compared to WS 3, S 4 does have a measurable effect on the combat effectiveness of the unit.
So, f you're worried about hitting, go with spears (more attacks). If you're worried about wounding, go with halberds. If you're worried about surviving a few rounds of CC, go with swordsmen, I 4 and Sv 4+ do make a difference to I 3, Sv 5+
In my recent games (Yay!)
, Halberds were by far the most effective unit against high-T low-I infantry (like Orcs, Saurus Warriors, or Dwarves).
They did suffer from insufficient armour,
but if you get a few decent rounds of hits in, wounding is much more assured than with the other core infantry options.
So yes, a Heavy Armour upgrade to halberdiers would make them far more viable as troops. Given the fluff of The Empire with lots of battles against Orcs and for example chaos beastmen, it would make sense to field halberds again.
So I agree. Heavy Armour is the way to go.