Note: I think you should have started your post stating that you work for Google. It's relevant information in this context.
3) iCloud Photo Library is not encrypted client side in a way that prevents Apple from decrypting it on the server, so like Google Photos, Apple will have your photos.
Having the data is only one part, the other part is what you can do with the data. Google's rights are extremely broad, although they conveniently did not put most stuff in the privacy policy:
When you upload, submit, store, send or receive content to or through our Services, you give Google (and those we work with) a worldwide license to use, host, store, reproduce, modify, create derivative works (such as those resulting from translations, adaptations or other changes we make so that your content works better with our Services), communicate, publish, publicly perform, publicly display and distribute such content. The rights you grant in this license are for the limited purpose of operating, promoting, and improving our Services, and to develop new ones. This license continues even if you stop using our Services (for example, for a business listing you have added to Google Maps).
Source: https://www.google.com/intl/en/policies/terms/
tl;dr: Google can keep your data, even if you stop using their services. Google can use your data for promoting their service and in new services.
I don't think most people realize that there is no way back: once you store your data (e.g. photos) in a Google service, it's theirs to keep (how that works with Dashboard, I don't know).
Please show me comparable terms for Apple Photos (Apple can keep your stuff forever and use it to promote services). If they are not there, there is clearly a difference between storing photos in iCloud or Google Photos.