It's ironic that in a time when the browser used matters less than ever thanks to good HTML5 standard support and differences lie more in the fringe, most recent corners of the living standard, the user agent strings are more detailed than ever.
It would help if the browser vendors, particularly Google, took a step back and spent some time thinking about why user agent strings were invented. They're more like cludges to know how to present a web page, which are less needed nowadays because you can request things like mobile device dimensions, provide HiDPI resources that are only used in case they are needed, provide entirely different views depending on mobile or web, etc. All without peeking at that ugly string. Beyond that, we have polyfills and frameworks that guarantee cross-browser compatibility and minimum supported versions, again without resorting to peeking at browser engine build numbers or worse because the detections are now largely integrated in the standards themselves.