It would be nicer still if they stopped thinking their browser only needs to get new features once per year. Safari is rapidly getting a reputation as the new IE6. Fully supporting ES6 means nothing when everything is being transpiled and minified anyway, and the (arguably) dominant mobile browser your (kinda) forced to target doesn't support features that shipped in every other browser years ago, heck many missing features have even stabilised in other browsers years ago. The dev builds on desktop are just a token gesture that further displays how far behind the times WebKit/Safari/MobileSafari are falling.
Here are just a few things not supported in any Apple browser, Including the "Technology Preview" on desktop:
CSS Motion Path; CSS Device Adaptation; Client Hints: DPR, Width, Viewport-Width; inputmode attribute; MediaRecorder API; Network Information API; Web Animations API; Pointer events; Web App Manifest; seamless attribute for iframes; Payment Request API; Credential Management API; Push API; FIDO U2F API; Permissions API; Screen Orientation; Object RTC (ORTC) API for WebRTC; Proximity API; Ambient Light API; Battery Status API; Vibration API; Web MIDI API; getUserMedia/Stream API; WebAssembly; 'SameSite' cookie attribute; Public Key Pinning; XHTML+SMIL animation;