Does Christian theology predict that I can't eliminate suffering from my life, because I cannot eliminate sin?
Does Buddhist theology predict that I can't eliminate suffering from my life, because I cannot eliminate impermanence?
Would a truly happy person then falsify both religions?
I refer to the religions as they are - but it does seem most religions undertake special pleading where they're not allowed to make mistakes or be corrected. This, despite several corrections in Christian theology in historical document, and I would not be surprised to find the same for Buddhism. They evolve/change, ironically due to impermanence.
If you need a definition of 'happy,' just interpret charitably until it works; though I'd take it kindly if you'd let me know what definition you end up with.