After 10 days of frustration I've gone back to the Adobe CC plan.
I tried 2 applications, the Luminar 3 I mentioned earlier seemed fine to begin with although saving an image was a bit slower than LR but gradually became slower and slower in exporting. Also my Nik Software plugins, specifically Silver Efex opened easily in Luminar but quite suddenly stopped doing it.
I tried another application, ACDsee which was slower in other areas but the main problem was that clone stamping was missing in the Mac version but present in the PC version. I tried it on my games PC which I didn't really want to use for anything else but the image rendering was horrible in my eyes.