Not that tough when your opponent is on your turf and fighting multiple enemies.
Sure it is! The overwhelming bulk of the German's combat capable forces until 1944 was in the East and even at it's lowest point (in the winter of that year) was never below 60% committed. The number of mobile formations the Germans had in the East on June 22nd had the almost as many men as the
entire German force deployed at Normandy. And the disproportionate distribution of German forces is reflected in the disproportionate distribution of where German casualties were suffered: 80% on the Eastern Front.
The Soviet didn't amass 7-10:1 numerical odds by the Germans getting forces drawn off to the west or just outnumbering the Germans in general. They got those odds by being smart, utilizing deception, encircling then destroying German armies, and generally being better at stuff that was relevant to actually winning wars. Meanwhile the Germans thought tactical competence alone could carry them. We all know how that turned out for them.
The Germans pulled it off in late 1944 and again in 1945.
Pulled what off? The Germans failed to stop the Red Army and WAllies from invading the Reich and destroying it completely.
They did it multiple times on the offensive against the Soviets,
Kinda. The Germans were better on the attack then the defense ultimately because their strategic intelligence was shit. The Germans had decent tactical intelligence. Units in the field performed solid reconnaissance, and their electronic warfare section was good at tracking enemy signals in battle. But it was all intended to find which hill the next tank was behind. The problem is that while you can attack without good intelligence (although it's certainly not advised), it is nearly impossible to defend without good intelligence (or failing that, superior force that allows you to recover from enemy blows).
with the Kursk offensive being an exception
Really, had the Germans ever tried to launch another major offensive they would have found it was actually the rule from that point on. In 1941 and 1942, the Soviets were taken by surprise from a mix of failing to coordinate their considerable intelligence assets and Stalin being stubborn. From 1943 onwards, the Soviets had gotten their intelligence collection, countermeasures and deception all sorted out and were able to run circles around the Germans as a result. One of the notable things I recall about Kursk is that when the Soviets first assumed that the Germans were going to attack there, they didn't just rest on that assumption because they remembered what happened when they just assumed the Germans would attack Moscow the year before. They made sure to
confirm their assumption and to do that they devoted considerable time, attention, and effort to their intelligence services.
The Soviets had the intelligence advantage from having their civilians behind the lines reporting and traitors on the Germans general staff leaking info.
All this means is that the Soviets ultimately appropriately invested in and coordinated their intelligence networks while the Germans did not. This is not a point in the Germans favor.