Lots of alternatives. As I said, use an external disk or iCloud. Or, use a different app.
Personally I do use iCloud Photo Library with good results. I have my library on my MacBook, my Mac Mini, my iPhone, and my iPad. All are completely in sync and all original photos are both in iCloud and on my Mac Mini's external disk. The other devices use storage dynamically so if space starts getting low, photos are removed from local storage but still accessible from iCloud on demand.
Photos works great if you utilize the features they've provided. If you want to roll your own solution that's fine, but perhaps Photos isn't the app for you. Or, maybe you need to purchase a computer with enough storage for the stuff you want to keep on it.