You arent doing something wrong lol, it kust takes quite a bit of grinding. Its always worth it in the end. My diamond armor has mending and it never even looks damaged.
yes but as a Minecraft bedrock player it is very hard to get mending books so its easier to just use iron enchanted or get some Dimond tools cheep from villagers
yes but i have a maxed out fishing rod and i have fished for around 1h+ and the only mending books i have gotten are mending on stuff like fishing rods or bows that you fish