If only. sudo, as configured out-of-the-box on Ubuntu, gets out of your way and lets you work (Except if you haven't properly authenticated in the last 15 minutes); polkit is similarly out-of-your-way.
Sudo is also (relatively) easy to configure: "this command line can be run under sudo by anybody", "this command must not be run under sudo even if they know their password", etc.
UAC is always-in-your-face about everything, often unexpectedly - it hijacks your desktops at inopportune times, and there's no way to tell it "Yes, this software can do this again for the next 15 minutes without asking me again".
UAC is very, very far from being the graphical popup equivalent of sudo. If it had been, people would not have complained as much. (Someone always complains. But in the case of UAC, most of the complaints are justified)
Not true: UAC only pops up for apps that need to access a file/registry key, etc. that affects system-wide behavior
"... often unexpectedly - it hijacks your desktops at inopportune times ..."
This isn't true: UAC pops up precisely when an app is launched that needs to access/modify a system-wide resource. If you're running apps that OFTEN need to access system-wide resources, you could choose to run them as admin and avoid the UAC pop-ups ... while also hoping that those apps are not malicious or over-enthusiastic about "helping".
"and there's no way to tell it "Yes, this software can do this again for the next 15 minutes without asking me again"."
There kinda is - just run the app as Admin. It'll then run with admin rights until you close it.
Of course, without specific examples of what you see as erroneous behavior, I've posted what are, I am sure, inadequate responses to your specific issues. If you'd like to share you specifc issues, I am sure we could have a more fruitful dialog and who knows, I may be able to carry your case internally to see if we can improve things in future OS releases (no guarantees here other than my trying my best).
While what you say was true about Vista, in Windows 7, 8, 8.1, and 10 UAC prompts are suppressed when they're the direct result of user interactions within the OS itself. Each OS reduced the number of UAC prompts a user experiences.
They also broke the security on the default configuration because now you can just interact with the system components to bypass UAC, see e.g. [0]. This is officially not a security vulnerability because UAC isn't actually a security barrier unless you set it to "Always prompt", but just a feature to make applications play nice. But note that it's not on "Always prompt" by default...
Sudo is also (relatively) easy to configure: "this command line can be run under sudo by anybody", "this command must not be run under sudo even if they know their password", etc.
UAC is always-in-your-face about everything, often unexpectedly - it hijacks your desktops at inopportune times, and there's no way to tell it "Yes, this software can do this again for the next 15 minutes without asking me again".
UAC is very, very far from being the graphical popup equivalent of sudo. If it had been, people would not have complained as much. (Someone always complains. But in the case of UAC, most of the complaints are justified)