(spoilers) I just found an easy way to fight armored lynels.

1. Eat attack up food (1.5x dmg)

2. Attach something blunt to a Royal claymore (moblin horn, lynel mace horn etc), and flurry rush an attack (2x dmg on flurry rush for royal weapons) . Armor melts in one flurry rush. (Any royal weapon works)

3. Use a royal guard claymore thats almost broken fused with a lynel horn. Does like 170dmg, and if you only hit him when mounted it uses no durability.

4. When his health is super low swap to a different weapon. Otherwise you might accidentally hit the ground and break the sword.

Best fuse items for weapons are from lynel drops... (55 attack from silver lynel)