Much as it would be nice to reclaim the language, I don’t think it’s possible.
As you have observed, many people still use the two words interchangeably.
Transactivists actively encouraged that interchangeable use in law (the GRA being the obvious example) in the full knowledge that it would build in confusion.
They set about changing the meaning of the word. This was not accidental.
It is in some ways very similar to the way they are trying to change the meaning of the word woman to include some men, because changing the meaning of words used in law is a short cut and much easier than arguing for those men to gain the right to use women’s spaces through open debate and changing the law itself.
So if politicians and those high in the civil service and others in positions of power are using gender to mean gender identity and we ignore that change or spend our efforts in every case checking the language to see which it is being used as, or whether it’s deliberately being used to sow confusion, then we end up fighting an increasingly obscure argument.
Whereas if we insist that the word which has a clear and unambiguous meaning is used whenever it’s important, we can be much clearer over what we are arguing about. To which end, no it is probably not worth correcting people on threads talking about “gender reveal” precisely because it’s not important. In addition, I think many people would just roll their eyes and think it is precious, which is the opposite of what we want.
Once it is fully established in law that segregation is by sex, for example, then we can leave the words to evolve in a natural way and we might see a natural reversion to the common meaning.
But I don’t think what you are proposing is possible, OP. Language is being deliberately manipulated by those pushing gender ideology and I don’t think we can easily push back against that aspect, other than to hold firm on the meanings of words that ought to be utterly clear, such as the words women and female. Those are much more important words to protect.