Problem is that by the time the German AFV industry gets back in action again in 1955-1960 the writing is already on the wall for the heavy tank. The other western heavy tanks start development in the late 40s/early 50s and are recognized as being obsolete before they are even deployed.
The Leo1 started out as a 30 ton Tank
Leo2 is now approaching 70 tons.
In WWII speak, that's a heavy tank, but one with decent mobility and reliability: that's what was new, but still has all the heavy tank disadvantages like bridges. The Tiger I and M1A2 have roughly the same ground pressure,the Le02 slightly less-- but overall weight is still there
The difference is in their version of Chobham, which adds a lot of weight, and a lot of protection.
The weight difference going from a 105mm to 120mm is minor in comparison, roughly a half ton.
What's going on for the original PoD, WI the West Germans make a Heavy Tank? the building blocks for what's needed for a reliable Heavy tank were there in the late '50s when the Leo1 was being made. The British 120mm was far lighter than previous 120mm guns. High HP, reliable Diesels were around.
The Germans and French had a close defense relationship at the time, and it's unlikely the Germans would have been unaware of the plans for the French 105mm F1 cannon, that would use a very powerful HEAT round, rather than APDS or APCR. The US was working on HEAT shell for the 90mm, very similar to the French Orbus G, using slipping driving bands rather than the outershell and ball bearings, as used by the French. The research on that began in Germany at the end of the War.
So they would have known Powerful HEAT rounds were on the Horizon, and should have protection against them, as well as the RPG-2 all over the Warsaw Pact Infantry. The British were working on their 'Burlington' Armor to increase protection, a very closely held secret on the details, while the US HCR program was out there for anyone who wanted to read period documents from the War.
