Learn English – Is ‘but rather’ considered grammatically correct

adverbsconjunctionsgrammaticality

Is this comment that I made here grammatically correct?

In Latin, when a group of males and females is combined, the neutral plural form is not used, but rather the masculine is.

In:

In Latin, when a group of males and females is combined, the neutral plural form is not used, but rather the masculine is.

'but rather' is perfectly fine and a good alternative to:

In Latin, when a group of males and females is combined, the neutral plural form is not used; rather the masculine is.

'Rather' is like 'instead'; using 'but' allows it in one conjoined sentence rather than a separate one.