If you're developing for Chrome first, it's hardly surprising that a browser made by a company which takes a much more conservative approach with user privacy and device efficiency isn't going to just adopt every half-baked API the Chrome team throws out there.
Does Safari lack support for some actual standards? Sure. No browser is "feature complete". The difference is, a good chunk of what people complain about, are draft features, made available in Chrome because Google's whole business model is "put everything in a browser, and track the bajeezus out of it".
Does Safari lack support for some actual standards? Sure. No browser is "feature complete". The difference is, a good chunk of what people complain about, are draft features, made available in Chrome because Google's whole business model is "put everything in a browser, and track the bajeezus out of it".