Qubes implements a Security by Isolation approach. The assumption is that there can be no perfect, bug-free desktop environment: such an environment counts millions of lines of code and billions of software/hardware interactions. One critical bug in any of these interactions may be enough for malicious software to take control of a machine.
Should we all use Qubes OS for most daily task that involve the internet?
I have been using Qubes OS for all my online activities for the last few years.  Qubes' disposable VM concept fit nicely in this use case.