iOS (and macOS Safari) only has the stupid "declarative blocking" functionality which is trivial for ads to bypass. In addition, it often breaks websites because it can't inject runtime code (like uBlock filters can) to substitute malicious JS payloads with neutered versions that still expose the same API so the rest of the JS doesn't error out.
Injecting code via Web Extensions is too late for reliable blocking - by then, either the malicious JS you are trying to defuse has already ran (if it wasn't blocked declaratively), or if not then the rest of the page's JS depending on it has already exploded and "fixing" it after the fact (by substituting a neutered shim via Web Extensions) doesn't fix the rest of the page.
No, it really does not. My iPad with safari and safari filters next to my android with firefox + ublock is nowhere near as comprehensive. Even news websites sneak ads into safari.
Safari does actually support CSS selectors in its content blocking API. However, see my other comment on this very subthread, it's nowhere near enough and is trivial for ads to bypass.