Good reason for strict purchase limits

[Weasel]

Just got my butt handed to me by five panthers, no infantry, no artillery, just five panthers with good fields of fire. The discouraging thing is I am suffering the same fate in another battle where once again my opponent only has panthers. Those five panthers stopped cold an infantry battalion with a troop of armour supporting coupled with 4 air strikes and 3 artillery batteries.

This brings up two points for me:

1. strict rarity must be used to even things out more; and
2. it seems the German players can only play if they have the very best armour, you never see PzIVs.