I don't understand the argument at all. Why is weapons delivery by other states than Germany permissible but not for Germany. Why does it matter where the weapons delivered come from? I could accept being for or against weapons delivery, but how can you be both?
Gysi is certainly a little more strict than other politicians due to party politics, but basically, the German stance across all democratic parties is: we acknowledge the right of Ukraine to defend themselves and we are willing to help, but it would be bad to deliver German weapon systems directly to the Ukrainian battlefields.
Why is that?
Well, no politician has officially come forward and said it into a camera, but German equipment is pretty distinct. Germany build/t their own tanks, for better or worse. You can recognize German equipment as German in videos. There is plenty of video material of German equipment manned by Germans, driving through the landscape of eastern Europe, especially Ukraine and Russia (both being part of the Soviet Union at that point), waging war, pillaging, destroying, and killing. Those WW2 images are iconic. German tanks rolling through Russia. If you have any western TV stations, if you switch to their respective "history channel", there is a good chance you can watch them right now. The pictures are 70 years old and still people watch it.
It is part of the German self-image that never again should German tanks roll through foreign territory. That image gets a little blurry, when NATO parter Turkey has their (German made) tanks roll into Syria or Kurdish territory, but it is the general thought that counts and after all, German tanks never rolled through Syria before, so there is no side-by-side footage of Nazi tanks and modern German tanks invading Syria.
Now Ukraine? Oh yes. If German main battle tanks rolled through Ukraine shooting at Russians again, Putin's propaganda machine would have a field day. Finally, they can show their material of the Nazi invasion of 1941, in parallel to German tanks rolling through the very same plains in 2022 and explain how they were absolutely right from the beginning; this is a war against "the Nazis" all over again and they have proof. "Denazification of Ukraine" sounds phoney, but if you can show German tanks rolling in the general direction of Russia, people will recognize the tanks as "German made". German tanks are rolling again. The Nazis are coming. That is a very simple and very much practiced narrative that you can call up in a heartbeat if given the chance.
So the solution seemed to be that Germany delivers German tanks to eastern NATO allies, so they in turn can deliver their Russian-based tanks to Ukraine. In theory a win-win. They get modern tanks, Ukraine gets tanks compatible with their logistics and Russia is denied their propaganda coup. Because Russian tanks look Russian. Russians know their own tanks. You cannot really rekindle the "Nazis are coming" image with a Russian tank fighting another Russian tank.
So this is one reason why politicians in general in Germany are open to give logistical help to Ukraine, but they are very reserved when actual, recognizable German weapons, especially tanks, are concerned. There is a huge difference between a German made tank rolling through Ukraine and a (let’s say) British made tank rolling through Ukraine as far as the propaganda images are concerned. It does not matter whose money bought them, but how they look.