Peng's letter also 另有故事. To me the letter was more political than anything else.
What Liu did and said in 大跃进 were against his thinking and ideology. Why Liu did it? Without what Liu did in 大跃进 and Peng's letter, 中国或不至于...I agree.
This is just my opinion. Zhou Enlai understood what went on and that was the reason why Zhou followed Mao in CR.