Nothing says they didn't.
It is like being told that someone went to University and got a masters. And then you claim nah they didn't study, they didn't even do an exam or write a thesis, they simply walked into the University premises and acquired a masters because they only said
they went to University and got a masters.
You can't know exactly what happened merely from a conclusion because it lacks details. WCI can literally be abridged as going to WCI to get a Poneglyph, take back Sanji and then leaving. While it isn't wrong, it just doesn't detail everything that took place.
They weren't friendly rivals, they were enemies. They wouldn't have fought each other if they weren't enemies.
They just respected the other outside of battle. Even Shiki states that Roger was a wall that stood before himself and Whitebeard. Even Shiki was an enemy of Whitebeard, it's just outside of battle that they can be courteous to each other. Doesn't mean they wouldn't kill the other in battle when their agendas are in play.
Only reason Roger and Whitebeard are seen together in the end was he was going to die, his crew had been disbanded, he'd already become Pirate King... there was no reason to fight, he came there to inform Whitebeard on some information.
We didn't, Usopp's statement there was a joke because it's unrealistic. It's impossible to do so without fighting. Otherwise there'd be no need for the time-skip for the SHs to grow stronger.
Law said this about entering into the territory of the Emperors. Impossible to do so without fighting due to the sheer size of the territory and the number of subordinates.
We've already been to WCI. No one can just go into WCI undetected. The whole territory especially the sea is monitored by sea slugs and innumerable number of homies.
Sensible and reasonable guesses. It's like saying that it's reasonable to assume that someone just walked into Impel Down and escaped without fighting anyone. Highly unlike. It's the case when one enters into the territory of an Emperor, it's only a sensible and reasonable assumption to assume there was some sort of exchange and conflict.
Even if we don't know, chances of simply going to WCI and not fighting or being detected, highly unlikely to the point of being an unreasonable assumption.
Big Mom wouldn't even know Roger read her Poneglyph with VOAT had she not seen him there. That's the kind of statement that proves they must have met the other during his time in WCI. If someone read your diary and then sneaked out undetected, there's no way you could deduce that someone read your diary unless you saw them do so. At the very least, Big Mom and Roger met during his time in WCI. Highly doubt she just stood there and let him do as he pleased.
You don't stop being an Emperor for losing. Manga has never said this.
Shiki also lost to Roger, didn't stop him being the top 3 Pirates or Emperors during Roger's era. Kaido also lost 7 times and has been captured 18 times. If losing stopped someone being an Emperor, Kaido shouldn't be considered one at the very least with that record.
So does Luffy, doesn't change the fact he still needs to be strong. It was a sea battle, not a hand to hand battle. No luck in hand to hand battles. No amount of luck would have helped Luffy defeat Katakuri, only strength, thus why Rayleigh trained Luffy. It's impossible to defeat others without strength.
Only role luck plays is in circumstances like the weather, timing, but not hand to hand combat. Luffy being in the same prison as Grandpa Hyou or Kawamatsu, that's luck because now he has acquired 1 of the 9 scabbards and Hyou gives them access to 5,000 Samurai. Luck is circumstantial, strength is the only way to defeat the strong and that's absolutely necessary.
WCI wasn't meant to be a fight to defeat an Emperor, but rather, to save Sanji. WCI doesn't imply anything about Luffy not defeating Captains. All Oda did was change Big Mom from being the main antagonist to fighting and having Katakuri being the main obstacle. He still intends to return back for Big Mom. Luffy's still growing stronger.
When there's no reason for him to fight Katakuri again, no one left but Big Mom.
Well, if you read the Vivre-card:
He's not, his strength is only 2nd to Luffy's. As is established, the captain is always the strongest. There's absolute reason to believe Luffy is stronger as he's defeated the strongest opponents in every arc while Zoro tends to take on the 2nd strongest.
Pretty much conclusive that Luffy will definitely defeat the Emperors. He's still growing stronger. Unless you can prove that Luffy won't grow stronger than he currently is, then being koed by Kaido is irrelevant. Luffy tends to lose initial battles and then comes back either more composed or stronger. He's yet to Awaken and we know his Haki will definitely improve this arc.
You can choose to think otherwise, but it seems pretty clear whether we like it or not.
Actually is.
Whenever a character remembers a character who defeated or humiliated them in some shape or form, the scar they got from that person aches.
- Chinjao's scar aches when he remembers Garp.
- Luffy's does when he remembers Akainu.
- Tamago's does when he remembers Pedro.
- Shanks' aches when he remembers Blackbeard.
Unsurprisingly, Whitebeard's scar arches when he remembers Roger. Implies he defeated him.
He actually never has. If you hit a character and they make this expression, it means you're just as strong as they are or maybe stronger. As long as you can do damage to a character with your physical strength, then they're not superior that superior to you.
Only time Luffy has come close to defeating a character stronger than himself was never. That's why Luffy couldn't even stand toe to toe with Admirals pre-skip. Strength is important. Moriah was the only opponent that was defeated by a team-effort, every other opponent outside of that was due to his own strength.