When temperament researchers are added the concept of "goodness of fit" to their theories, they left one meta-theory behind and endorsed a new one. which new meta-theory did they endorse?

The answer is maturational meta theory. This theory was introduced by Arnold Gesell in 1925. A child's development is subjective to both environmental and genetic factors, but is largely influenced by the child’s physical development. With long term bad fit child's temperament will get worse.