Wait, what? Are Windows, macOS and OpenBSD also the same OS in a different shirt? What do you consider a different OS then?
What is your goalpost for a "serious OS"?
What market share proves is popularity. Which is important in an OS, but ridiculing other people's choices on grounds of market share doesn't seem very convincing to me.
Doesn't make you right. PostmarketOS and LineageOS are very much NOT the same OS in a different shirt.
Don't try to be provocative just because you were wrong, it doesn't help.