I'm sorry, but your "recommended answer" is entirely untrue.
1.) If you upload photos to iCloud Shared Photo Albums, you can completely delete them from your local library and they will remain on iCloud in the shared album.
2.) iCloud Photo Library uses a LOT more local hard drive space than storing the photos locally, even with that "optimize local storage" option turned on. I don't know why it does, but a few weeks ago I enabled it on my iPhone, iPad, and Macbook, all of which had between 1GB-2GB of photos in their libraries. Without my adding any photos, my iPad photo library has TRIPLED in size to over 4GB, my Macbook photo library increased to over 9GB (!!!). I haven't checked my phone in a few days but last I checked my photo library on there had swollen to immense size as well. All three device's hard drives completely were filled by this. I've checked and checked again, they're all set to optimize local storage. In fact I can't use iCloud photo storage AT ALL on my Macbook anymore—as soon as it devoured all the free space on my hard drive so I only had 1GB left free, it disabled the iCloud features and now I amspending 9GB of free space on an iCloud Photo Library feature that I'm completely unable to use... I'm unable to use either iCloud Photo Library or iCloud Shared Photo Albums, or see the photos stored on them from my Macbook.
iCloud's photo features are very seriously broken, almost entirely unusable. I'll refrain from further editorializing, but as a matter of practical advice in direct response to your question, I'd say, there are plenty of cloud photo hosting solutions that work, I stick with one of them and recommend that you just do that, too, rather than inconveniencing yourself by worrying about iCloud photo "storage" in any way.