You can now easily transfer photos between iCloud and Google Photos
There are now tools from both Apple and Google available that you can use to move your photos between ecosystems.
mobilesyrup.com
A new data transfer tool makes it much simpler to switch between iPhone and Android or vice versa.
This tool is backed by the Data Transfer Initiative and basically aligns Google’s and Apple’s main photo library apps behind the scenes, making it possible to move a full library from one app to another.
You can still use the setup tools in both phone ecosystems to transfer photos, but this is for people who want to do it post-setup.