What do you feel when you want some fresh air and install a new browser, but feels the same. Even the setting menu is as empty as Chrome.
What are those unique functions that you miss so much?
For example I remember that Vivaldi Mobile in 2020 can save the whold webpage locally. I use that to store html books to read them offline. But now this function just disappeared from the menu.
So naturally it's going to coalesce and standardize around 1 or 2 options. And this is what has happened with Chrome and Safari.
That's not to say that no one can make a better browser or that they shouldn't try, just that its a huge undertaking against a well-entrenched technology and those are very difficult to pull off.
To answer your question about functionality, the browser today is capable of being a full desktop app. It can do anything a desktop app can do. So what you're really looking for is not a replacement browser but a web app that saves pages as HTML, etc. It actually makes more sense from a development standpoint -- and ultimately benefits users -- to have the functionality come from apps and not the browser itself.
If the developers didn't do that, then you'd have more than a few users complaining that it's not like browser x so it sucks.
As for functions that disappear, I wonder if those are functions that the devs discovered (via telemetry or some other magic) that a majority of users didn't take advantage of. Why maintain them when most people don't use them?