Beta guy + fat chick can be successful insofar as it will be more sustainable than beta guy + thin chick or alpha guy + fat chick. But that doesn´t mean that it will result in a truly happy couple.
Also, note that the “Alpha” vs. “Beta” distinction in men is largely internal, a matter of outlook and behavior.
That is where it gets tricky, doesn’t it? Women are judged primarily for their looks and men for their wallets. Both are fleeting... or can be. Reminds me of a woman that was assigned to my Mother (who was a R.N.) The woman was stunningly beautiful.. worked out everyday and had the plastic surgery to make herself more glamorous to her wealthy, Alpha husband. The woman had both breasts removed due to breast cancer. In recovery, her husband told her he was leaving her and that he “couldn’t stand to be married to a freak without T*ts”.