Can you post the exact errors you are seeing? Unfortunately, these are most likely bugs in Safari itself. Apple does not seem to care much about WebGL (or web standards in general). Safari can’t even run the WebGL conformance tests without crashing the entire browser (let alone pass them).
As for mobile Chrome, it’s actually just a wrapper around Safari because Apple doesn’t allow custom rendering engines on iOS. If it doesn’t work in Safari on iOS, it won’t work in Chrome or Firefox on iOS either (because it’s all using Safari under the hood).
I recommend anyone who wants to see Cesium (or WebGL in general) run better on iOS file bugs with Apple. If any of the cesiumjs.org examples no longer work in Safari, they might be more likely to fix those (since they are regressions).