Try making the same claim using a thrift store laptop for < $200 which is all the computing power a whole lot of people have access to (if any). Yes computing is fine (and a little better than 20 years ago) for software made and used by wealthy people. You have to slide down the curve a bit to discover the frustration with everything being terribly hungry for ever-increasing resources.
Of course if you upgrade to a top quartile computer every few years you're going to have a relatively good time.
$200 computers obey Moore's law too.
But even with LibreOffice's clunkiness, I still use it at home. While I am partial to Apple Keynote for presentations, I prefer LibreOffice Writer and LibreOffice Calc to Apple Pages and Apple Numbers, respectively. And whenever I'm on a Linux or FreeBSD machine, LibreOffice is available for me to use, while iWork and Microsoft Office are not options.
It has to support and parse a billion more formats. Including the fact that MS word file formats are in some cases literal dumps from word's memory (iirc).
Rendering things properly is also a difficult problem to solve. Look how difficult it has been for much of the 21st century, to get a webpage uniform across all major browsers, and then realised that you not only have to display the same across all major browsers, but also be 30 years backwards compatible.
While that is an additional load if you deal with those formats, the root of things like startup and runtime bloat lie elsewhere.
> Rendering things properly
These should not affect startup performance though.