Slitherine

It bothers me a bit to see people developing rosters of core units consisting largely of units that were quite rare in the actual war. Tiger II, for example. Tigers and Tiger IIs were the rarest tanks in the German army, never built in large numbers. And generally the ones in service spent less time fighting than the more common medium tanks due to transportation difficulties, there were only a limited number of bridges that could take the weight and special measures had to be used to get them on rail cars. Yet we see people listing core forces on the forums where half the force and all the tanks are Tiger IIs.

Perhaps in addition to cost, unit types could be assigned a rarity factor. For example, units might be very rare, rare, uncommon, or common. Each rarity class might be assigned a max percentage of the force, for example 5% for very rare, 10% for rare, 20% for uncommon, and unlimited for common. If the player tried to buy a unit that would be in excess of the rarity factor, the system would disallow it ("So sorry, Herr General, but our factories haven't produced enough of that type yet"). Rarity factor might change over time, for instance Panthers might be rare at Kursk but only uncommon a year later.

Deducter's unit chnges fixes this quite well

This is certainly the case on the easier levels where prestige is abundant. However on the higher levels I have very few Tigers as I have no money so I am very reliant on the special heroes and captured units I receive.

Yes, this is a subject that has received lots of discussion among the more historical minded. As Kirby said, Deducter's mods fixes this very effectively!

The devs are also conscious of this, but time and again there has been strong resistance to imposing strict purchase limits broadly across all skill levels. Perhaps in the future it can be tailored for different levels.

Also, unlock the higher levels and play on "Rommel," which is my preferred solution. You can still create an ahistorical corps, but it takes time and skill to do so; it will keep you challenged for many hours.