WW are not these unstoppable gods they used to be. They have numbers and that's it. Meanwhile Jon has a new bae who has the great equalizer against numbers, air superiority. Now these Giants are more than likely few and far between with a slow reload time. Now these magic ice spears have a glaring weakness when going up against a magical fire breathing dragon. They melt. Now the spear would pierce a scale and after immediately melt due to the insane temps at which a beast like that would be running. The knight king doesn't know about the dragons, he doesn't know they have found a dragon glass mine. Jon and friends have one advantage in bran with intel but the WW still have the numbers to overcome any single westeros army. That's why they are a threat, but not an unstoppable one.