(spoilers) I just found an easy way to fight armored lynels.
Eat attack up food (1.5x dmg)
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)
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.
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)
Attach a octo balloon to several shields (save your rockets ;-) ) float up and using a Lynel 3x or 5x bow with a bomb flower (only uses 1 arrow and bomb but shoots 3 or 5 arrows/bombs) will eliminate all of their armour in one hit. You need to come close enough to ensure that all your arrows hit.
Then just beat them up as normal, flurry/mount etc.
Food also does help if you want to speed this up (3x attack up).
If you have a Lynel bow with not so good stats, rock octos will reroll the stats when they "repair". But the weapon does not have to be damaged, they will still reroll stats. Usually after 1 or 2 rerolls you will get a 5x (remember each rock octo will only do this once per blood moon).
unfortunately they are still like rockets. They expire after one use.
They are also slightly slower to rise and maybe (I never did the check) not quite as high, but they still do more than enough to get up high to do the damage.
Btw i have 3x attack up and a 3 shot 32 dmg lynel bow. Took me 5 bomb flowers to get armor off. But i was a bit far. Every time i get too close the bomb flowers kill me ....
Also, dazzlefruits on arrows. These confuse the Lynel and allow you to run up to it to mount and do that attack. Or Puffshrooms - since it loses sight of you. (These obviously don't remove the armour, but they are an easy way 'in').
The other thing is that if you are removing armour using melee weapons, then "hammers" work better than everything else. Attach boulders/rocks/spiked balls (talus hearts/construct dodads) to weapons as armour removal.
Unrelated to the Lynel fight, but popping a single Dazzlefruit also nukes ALL stal-enemies in the immediate area. Super useful if you get ambushed by a group of them and don't feel like fighting. You don't even need to aim at them directly, just toss the fruit on the ground.
oh yeah, you do have to be careful of that. and you do need the arrows to hit. Move to where such a shot will spread hit the lynel (side on is a good starting point - like the lynel is a barn door!).
Also if you are not all fooded up etc and/or wearing the Fierce Deity set armour it will probably take two shots, but this is still a cheap investment for the lynels demise.
Also, honestly its been a while since I started so most of my bows are 5x 40 (or close to) because I kept rerolling them.
Also anyone interested, if you hit up a white or silver lynels, you can usually kill 2 of them with one bow. So you might lose a bow, but you will get 2 in return, netting you +1 new bow and a replacement for the lost one.