Photos - deleting from icloud does not delete from other devices

Hello again, I have just noticed that of the many 1000's of photos I have in cloud, there are only around 50 on my mac? In the photos app, it say 20000+ only 52 on this mac. Should I assume my photos have vanished or am I try and download them individually from icloud. They were always on the mac in the first place before icloud. I have lots I want to delete. I thought deleting from icloud would delete from other devices but it is not. Surely you can't be expected to delete manually x 3 times?? Also, when I try connecting my ipad and iphone to the mac, not all photos are imported, just some here and there. Really get my head around this, any help greatfully received.