Safari does not receive any feature updates throughout the year, and it only gets critical bug fixes. And yes, it is bad when the competition updates regularly, fixes smaller bugs, and adds web features. Safari’s lack of updates causes websites to break or have to deal with different versions of technologies. It’s annoying as hell.
The Safari version that receives frequent updates and fixes, is the Technology Preview, which is mostly used by developers. However, the average user doesn’t use it, and it’s quite buggy at times.
So yes, OP is right. If you want an up-to-date WebKit-based browser, it’s either DuckDuckGo or Orion. However, DDG has a mediocre amount of user features, compared to Safari or Orion. Of the three, Orion is currently the most feature rich WebKit browser I’ve used.