Imagine if Apple built in some Amazon Silk-like ties between Assistant and iCloud? Or if they do some local caching or if Sprint really does have this exclusively and its on 4G?
Amazon Silk-like technology may make sense for ecommerce content (yet to be seen), but it doesn't make sense for complex search queries. The longest time is probably spent in understanding the query and ranking results, not in downloading the content of the results. For the same reason, local caching makes no sense, except for some personal data, which Google also has access to (openly or secretly).