WhatsApp is pretty popular, but Google Photos?

The vast majority of people take a picture with the standard camera app and never look at the pictures again. You don’t need a non-native app for that.

Iphone doesn't let you search photos really - try searching for "photos of me skiing" or "igloo picture" and you'll soon find google photos is way ahead.

I just tried "igloo" in photos and it immediately showed the only picture of a snow fortress that I built with my kids 7 years ago. "skiing" also worked fine, as expected, but "Tom skiing" did not.

Since the first level implementation works fine, you're talking about a second level detail. Do you think this would nudge enough people towards using Google Photo to actually matter?

I very much doubt it.

Everyone uses iMessage in the US unless they are talking to people overseas. My friends group gets upset anytime someone isn't on iOS because the messages turn green.