I would not call them "fully-fledged desktop
PC" - at least not when you
compare to an AMD Ryzen...
Obviously, Pi is no match for a standard PC when it
comes to things like gaming*, video and photo
editing, etc. But it is now powerful enough to carry out many daily office tasks and even
support
two monitor setups. You might want to take a look at MagPi magazine, issue #85 -
there's an
interesting article that details a week of experience of using a Pi as a desktop at work.
*) However, I have setup Lakka on my Pi and it emulates 16 bit consoles and arcades (and
even some
32-bit ones) without problems.
Janek