Your honour, I plead unfamiliarity with the internal details of the unbuilt proposed E-25 and E-10 designs. The apparent truncation of the gun barrel on the drawing was a confusing factor. I place myself at the mercy of the court.
The E series were an attempt to unify German AFV construction. There would be just as many different models (E-5,10,25,50,75) but using as many common components as possible (the E-100 not so much). The E-50 and E-75 were intended to be almost the same but with different armour levels and possibly a different gun to replace the Panther and Tiger II. Similarly the E-10 and E-25 were very much a pair with the same layout and design features but to be built with different length, armour and gun.
All replaced existing suspensions (Pz IV, Hetzer leaf spring, Pz III, Panther, Tigers torsion bar) with Belleville conical spring external units and the same road wheels. The advantages were less hull machining, less need for specialist alloys for torsion bars, much easier to repair or replace in the field. Similarly many other fittings were common. So while the bulk armour structure would be unique, the many fittings which really add up in cost (money or hours), would be common keeping the cost down. Remember the Pz III and Pz IV built at the same time shared components like visors, cupolas, turret bins, tool clasps and tracks.
At least that was the intention. How much of that commonality would have survived testing and production is another matter.
