Well the glitch on allowing that is once a player gets rich ( after capturing a capital), he could spurge on these units and the game has no chance for recovery. These units are introducing new values and to allow the mass production of them makes them less “elite” or “special”
The issue is nations should all have the opportunity to buy these and that be an equal one in order to facilitate their use in games. To make them expensive puts them out of reach and to make a no limitation on them places them as common units… they are nothing of the sort. Heavy Tanks are time intensive and technologically dependent units. These are not like “Liberty ships” rolling off the assembly line. At Kursk, Hitler waited for months just to get a few hundred of these specialized units and had to stockpile and postpone Kursk till he had what he figured was enough to punch the soviet fortified lines.
I see two types of units: common and specialized. FMG is making replacement standard units, and also a number of these “special or elite” ones and a limitation of some sort seems correct and proper.
A land unit that attacks at 4 is a major undertaking for the game, especially since its costing less than 10 IPC to build.
The Waffen SS, Shock Armies, etc represent elite armor units and as such in the war these were very limited in terms of quantity so i don’t see why they should not have some limits and cost is not a barrier to purchase.