It's not only promised to us, it is done. Jesus said "It is finished" and scripture clearly tells us that not only includes his taking on all our sins for our forgiveness but also taking on all our diseases for our healing.
His hand of blessing is outstretched, but we must by faith and grace take from him. He will never force anything upon us. You can point to people who evidently haven't been healed and I can point to you people who have. Temporal and changeable circumstance doesn't change the unchanging truth of God's word.
doesn’t Revelation say only a small number of humans are going to saved?
Was the thief on the cross forgiven? Yes. Was he healed as in taken down alive and going about his way? No. We still on this earth experience the case and effects of it including pain, disease, and even the end results of our choices. BTW Paul asked {Three times wasn't it} to have the thorn in his flesh removed? What was The Lord's answer to him? "My Grace is sufficient for the day" posting it off the top of my head.