It wasnt breaking the armour that got them killed, it was bypassing the armour all together. Back of the neck was a weak point, thus the hook weapons. you would thrust past the knight only to bring the hook into the back of his neck. Shoulders was another area to aim for due to there being a small unprotected are to allow the wearer to actually move his arms more than a couple of centimetres.
Even those areas would be covered in maille, on the partial or "field" plate armors. The Gothic-period plate armors had articulated joints until these gaps were absurdly small, as well as having under-layers of flexible armor, and hitting them would require either amazing luck or tying the guy to a post so you could beat on him.
In general, striking the center of a heavy plate would pretty much insure that the blow would do nothing. Even hitting at a "soft" spot might or might not see great results - as even those points would likely require penetrating some armor or over-extending whatever body part was contained in said armor.
Aiming for unarmored spots sounds good when you're looking at a modern flak vest that only covers the front and back of the torso. (They're really only intended to make medical care easier and more effective, not to reduce casualties.) The ancient world did not build armors this way. Again, no matter what the movies show, those guys realized where the soft spots on their armor were, and tried very hard to cover them as best they could.
The real logic of the hook weapons was to pull a man off of his horse, and/or to cut the horses' legs, so as to cause the heavily armored fellow to a) hit the ground rather hard, and b) lose the mobility advantage that the horse offered him. This greatly increased the chances that you could run him down and beat him into the ground with hammers or something. They were also useful for unbalancing an armored man, and so preventing him from hitting you (at least until he could get up off the ground) - and the hook or axe blade behind the neck would work for that every time, even if the blade contacted solid steel.
Still, yes, heavy bladed polearms are more effective against armor than light longswords ... but not for the reasons you just described. They work better because it is possible to hit harder, and so to increase the chance of damaging the target (if you manage to hit one of the softer points and/or really land a solid blow), and they work better at attacking balance in order to stun or temporarily immobilize (during which time the target could be hammered into the turf).
Only in the movies do people wear 80 pounds of armor but leave a huge obvious hole with skin showing.
