Quite possibly you've shorted some of the windings but not all together, which means there are mismatched phase windings (an unbalanced motor if you will...)
If the motor is unbalanced, it will have heavy losses as the "Eddie" currents won't be in the steel but around the windings.
I'd be surprised if you got it hot enough to make the laminations be ineffective, that would take huge amounts of heat is have thought.
You could test this by rewinding it. Wouldn't need to to do a full pack of copper, just put in one strand for the full amount of windings... It'll behave the same but with higher resistance.
I think this is normally how motors die. You can see this in the small concentrated areas of burn where the rest of the motor is relatively un charred. You can see in your pics that most of the windings are ok, where some have got so hot they've fused and cremated the insulation.
When I wound transformers at uni, the professor had us put layers of some special insulating tape between the coil layers even though the wire insulation could easily take the voltage. I think this means that small shorts between adjacent wires have a relatively small effect. I've seen a few but far from all transformers use this method.