The production also increased much more than in the whole US. Basically Europe's goal was at least a million shells until the end of the year. And even when they might fall a bit short on that goal, the US -by it's own account- is still in the we can probably produce 20k per month from 2024 and onward stage of ramping up production.

the German Leopard 1 tanks currently in Ukraine are partially the second line of defense for the Bundeswehr

Yeah, that's bullshit. They had to find people (most of them many decades past their jobs in military) to even do the training because Leopard-1s were simply not a thing for a long time. The ones they are sending to Ukraine are refurbished trash sitting in some yard for decades, mostly out of Germany even.

The only still existing Leopard-1s in operation are found in Greece. Then there are engineering vehicles because they were still sufficient for their job. And when they weren't anymore (because tanks they would need to tow got too heavy) that's when Wisent1 were invented. Which is a commercially developed upgrade for Leopard-1-based engineering vehicles to improve their power to a level where they can handle modern Leopard-2s again. And before the Ukraine war there was only a single buyer: the danish army.