Doesn't that assume you _have_ all of the emails on your device on order to search them?

I know for a fact, Gmail on my phone doesn't have the ~15 years of email in my account downloaded. I bet that would take significantly longer to download than the actual search would would take to perform.

If the things to be searched aren't already on the client, a client side search doesn't seem too useful to me, regardless of how much compute power you have.