But that is the crux of the problem. Panther is also a tank destroyer that can be destroyed by tank destroyes while they are out of range. Usually, it's better to have range than armour in such case. Also pricewise it is more effective to buy a jackson than a panther.
There isn't a faction in the game that can choose between a Jackson and a Panther.
The Panther competes with the JPIV and the Panzer IV, the Jackson competes with the Sherman and the Scott.
As for the Panther/Jackson matchup, the Panther's armour doesn't do much, no.
What
does do a lot for it is its extra HP: it kills a Jackson in four hits whereas a Jackson kills a Panther in six.
In a head to head battle, the Panther has a slight edge.