Way better security model
Unified error handling
Clean install/uninstall (no rot)
Much faster and more capable version of XAML running on top of DirectComposition with easy DirectX interop
Native support for web apps
Resolution independence with no extra work
Easier to support accessibility tools like screen readers
Saner API design (no flags where only some combinations are valid)
.Net Native
Much better touch support
Cross-platform (xbox, holo lens, IoT, phone...)
Access to devices like camera, mic, sensors with high-level APIs (even accessible through C#/JS)
No P/Invoke required for C#
You completely missed the point of my comment. "Objectively better" means that it's better in all accounts, as otherwise someone with different priorities could perceive it as worse, making it therefore only subjectively better.
And UWP is not better in all accounts. It grants Microsoft more control over the ecosystem, which is seen as negative by pretty much anyone who isn't Microsoft. Therefore someone who doesn't care so much about the advantages that you listed could perceive it as worse.
So, UWP is not objectively better, it's only subjectively better, which is why yes, people can very much justifiably complain about it.