It shows Killer's mental state, eating a smile and being made into a laughing puppet for Orochi mentally destroyed him. 1+1=2, it's really not that complicated, I can't break it down any simpler for you.
You want to talk about physics but think Zoro is on the same level or better than Luffy who can inflate his body to the size of a giant, which had greater hardness than steel before haki.
Someone ask Killer why he decided to use an inferior weapons on the Onigashima Raid
nik87 knows better than him about his own fighting style.
Zoro searches out the best swords, stop ignoring One Piece, re-read it if you have to, not just the fight panels with Zoro.
We didn't have Roger's named moves till we did, you cannot prove a negative and a hectic war like Marineford where dialog space is precious was not a good place to list out the names, they are named in the games. Proof positive is Marco using a named attack against Big Mom's ship when he didn't use one during the war on panel.
If you say there is no clear line between high tiers and top tiers how are you putting someone as a top tier? Just say tiers don't matter at that point, which is fine to do, but don't arrogantly claim someone to be top tier in that case and then run away from defining it.
Waste of time explaining this any further. The tier definition is the only thing I want to carry on with, if the above hasn't convinced you, then I will let you carry on with your headcanon.