Vonbontee said, "Also, Cynthia couldn't get John to stop doing massive quantities of acid, or getting way too drunk when he wanted to, and apparently May Pang couldn't either. So I don't see that any woman could've steered him straight if he didn't want to be."
Cynthia and May Pang were (are) lovely women who nevertheless don't have strong personalities - and Lennon needed a strong personality. A woman who measured up to John could have set him straight (IMHO).