1) by not being connected to the network when I import photos.
2) it was a passible solution.
3) photostream was most certainly not positioned as only a temporary storage system. It was clear that it was temporary, but it was promoted specifically as a sharing method. It was not for seeding devices as it never pushed filed to any of them, nor did editing files on the photostream have any impact on files residing on those other devices.
4) I'm not sure you are understanding both sides of the argument, actually. Because there's more to it than you seem to realize. For example: knowing which device made an image. Yes, we do need that information, but the reason it has become important is because of the change in how photos are managed on Apple's side. By no longer making a distinction between local and cloud images there's no way to tell whether you're looking at an image that's on the device or a thumbnail of one that's in the cloud. The rollout of iCloud Drive potentially makes this worse by pushing a copy of each of those cloud files to your phone where you can't get rid of them without deleting them from the device and the cloud.
None of this is to say that the previous system was ideal or that the new way doesn't have any advantages. But there really are some fundamental issues with this approach that impact almost every aspect of photo management across the while Apple platform. If you're comfortable with the new system, great. Use it. Use the caramel corn out of it. Just be aware that no amount of reassuring me that "nothing has really changed" is going to change my opinion. Because it's blatantly obvious that a great deal has changed and a good deal more is yet to change with the rollout of Yosemite.