Modern browsers are application runtimes with a very flexible delivery mechanism. It's really up to web developers to decide what features this system should have to enable rich experiences for their users. Declaring that they should be functionally impaired or what they "should be" without taking into account the user experience we want to deliver is the wrong way of approaching this.
To be clear: I do think we should take security very seriously, especially in the one program people use the most. I also think reinventing operating systems to run within other operating systems is silly. But the web browser has become the primary application runtime and is how most people experience computing, so enabling it to deliver rich user experiences is inevitable. Doing this without compromising security or privacy is a very difficult problem, which should be addressed. It's not like the web is not a security and privacy nightmare without this already. So the solution is not to restrict functionality in order to safeguard security, but to find a way to implement these features securely and safely.