I do know that several years ago, my son had to be on pred for allergies and the doctors told me that it is not good to take it long-term. Now that was for a teenage boy, cats may be completely different. This is why you need several opinions.
The taking of any corticosteroid type of drug long term can create a multitude of problems. If used in the mouth it causes thinning of the tissue of the gums and palliate. After radiation treatment I developed an autoimmune disorder of the mouth that required the taking of corticosteroid drugs to keep my condition under control. I was limited to the time I could take the drugs because of the adverse effects. It would be the same for cats as well.