Is simplication of known results worth a publication?
In general, this kind of result might be worth publishing, also in top journals. However, it is impossible to tell without knowing the specifics. It might well be something that has been known as a "folklore result" for long in your field.

Luckily, you say that the leader of your research group is the major expert on this. So, ask him and not a random bunch of people from other fields you found on the internet.

If you have already asked and he disagrees, chances are that he is right. But if you disagree and insist that it is a major breakthrough, you can still write everything up, put it on arXiv, and wait for feedback from other researchers.