You are overestimating the success of the offensive based on Ludendorff's quote, a source I would not take well into consideration due to the eccentricity that Ludendorff displayed several times during the Spring Offensives. The reality is that the Germans
didn't break through, not because the American divisions stopped them at the critical juncture (not to take away from the heroic stand of the American forces), but they didn't break through anywhere. The reality of the situation was the main French defensive line, which needed to be ruptured to consider the battle a German victory, lay beyond the range of German artillery. When the Germans captured the bridgehead on the Dormans it represented their furthest success in the entire battle, yet they had failed to break the 6th Army as a fighting force. The Germans
did gain ground, but only by overrunning the outward trenches of the Allies, not by breaching a hole into the French defenses. Even if they had advanced further, they would've found themselves outside the range of their own artillery, leaving the Strumtruppen to defeat the 6th Army (now being reinforced by the 9th Army) by themselves. Such a task was beyond their capability.
And what should be remembered is the fact that the decisive moment in the 2nd Battle of the Marne was not the stand in Belleau woods by the 3rd Division, but the Allied counterattack on the 18th which was led by 44 French divisions.
You have failed to grasp the decisive untility of the breach of an enemy front. Once that occurs the sky is the limit, as it was when penetration by Allied counterattack forced the Germans into an eventual general retreat, and ended the war.
No, the issue here is you're overestimating the ability of the Germans to
exploit the breach. The reality is the Germans had breached the Allied lines before, but every time they had done so they had been unable to follow it up. At Yrpes the German usage of poison gas broke the British lines, but there were no sufficient German reserves to rush in to exploit the gap. In Spring 1918 the Germans had the same problem; they could break through by not exploit it. In Michael they achieved considerable success and ruptured the Allied lines in several locations, only to be bogged down by being unable to sustain their offensive because they kept running out of steam. The Germans were only able to achieve such breakthroughs by throwing together their best troops into their own formations and attacking in full force, but this cost them their best men while the follow up divisions were composed of second rate soldiers. The Germans as a result were losing their best men and their reserves were full of troops of inferior quality. In Michael, Georgette, Gneisenau and Blucher the Germans were able to breach the lines only for their offensive to stall because their troops became too exhausted and their logistics unable to support further advance. Why you feel it would be any different at the Marne is beyond me.