Obviously what Cierpinski did worked very well. But if the East Germans were, as the quote says, ten years ahead of all other nations with regard to effective training methods, and I'd even include doping methods here, it seems that they should have produced more top level distance runners than they did . They did well for a country their size but that happens now and again (New Zealand, Hungary, Finland). But I think the only other world class marathoner they produced was Eckhard Lesse whose best was 2:12, I believe, a time which plenty of runners from countries that were not ten years ahead of all others were running. Below the marathon there was Werner Schildhauer in the 10,000, Olaf Beyer in the 800, and years earlier Jurgen May in the 1500 and 5,000. May was a big "Lydiard" guy,the East Germans were very fond of Lydiard and brought him to the country more than once.
But you can't simply look at one big success and say the person who had it had it because his training was better than everyone else's. At the time a lot of Shorter's success in the marathon was attributed to the fact that he did NOT train like a marathoner but rather like a track man who also ran enough miles to do well at marathons and whose track training allowed him to toss in a sub 4:40 mile here and there which his competitors, who were not track men couldn't match. And Shorter was not physically whole in Montreal. He had trouble with his foot which was the beginning of the end for him. He was never the same runner after Montreal as he'd been before.
So yes, maybe Cierpinski used drugs and that was the reason he was able to beat Shorter. Or maybe it was because everyone who thought training like a track guy was the key were wrong that and training like a marathoner really was the answer after all, that it was Shorter had been the outlier. Or maybe Cierpinski was ascending at a time when Shorter was descending. Given what went on in East Germany you have to consider seriously the idea that he drugged his way to a win. But there were stories at the time which said he was really an outsider within the DDR's sport system and sometimes at odds with officials for his preference for going his own way. So maybe not using drugs was part of going his own way. He has not had the kinds of physical issues that many of the drugged DDR athletes have had in later life.