Losing =/= hearing someone out by choice. He already understood that Yamato had no ill will and he didn't come to that conclusion after conflict.
He chose to fight Yamato even knowing she had no ill will. He gave up on fighting her when it was not working. He didn't want to hear her out, she
forced him to, because he couldn't get past her.
"He was serious, but didn't go all out." Semantics. You can't claim Yamato laid out the opponent he was going to use Gear 4 against as a no diff, and then say Luffy lost when he deliberately avoided using that level of strength against the same Yamato.
Luffy was trying his hardest to get past Yamato without using G4. He's shown to be incredibly pissed off, he's sweating and he's huffing.
He's clearly exerting himself greatly.
Luffy's ability to take the cuffs off also was an immediate comparison of their Haki; Luffy's first mastered demonstration of internal destruction which Yamato clearly doesn't possess. So he didn't use his real strength of DF or Haki to force an outcome, instead decided to talk and then help Yamato. Sounds like an inconclusive clash if there ever was one.
Zoro can't use internal destruction, yet he could cut up Kaido. Even with internal destruction, Luffy's damage was "too shallow". It's not clear that Luffy did not use internal destruction against Yamato.
The battle was not inconclusive because Yamato achieved her victory condition: "get Luffy to listen to me" and Luffy failed at his: "get past Yamato". Yamato was never attacking Luffy, fighting back or trying to hurt him. Luffy giving up on fighting her is what victory looks like.
That's like Sanji was calling Mihawk "Strongest Man" back in Baratie but in context, we know he's talking about World's Best Swordsman.
