Stop expecting differently.
Of course you do. You can run GrapheneOS, or LineageOS, postmarketOS, or mobian, or many others. All of those are open source, you can modify them as you want before you flash them.
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.
And that I disagree with all the whining about having root everywhere. If you are able to install your preferred OS on the device you own, then you can install one that has root, or fork an open source one and add root, or write your own.