Luffy was a 100% serious behind every one of those invitations and if you don't think so, you don't know anything about Luffy. The fact that events happened after the fact to cement one of his invitations doesn't change that.
Then I'll repeat what I just posted to Robby:
"So, if you are ignoring the hints given by story and judging just Luffy's desires to make comparisons, then why aren't you considering the Luffy actually was bothered by Yamato asking to join his crew? Or that he still calls Yamato by a nickname even after witnessing him fighting Kaido, indicating a certain emotional distance between them?"
Luffy didn't know anything about Robin betraying Crocodile at the time. All he knew is she saved his life and then he saved her life so they were essentially even. He only let her join because she said she wanted to die and Luffy ruined that so he owed her that and he agreed. I also do not remember Luffy going out of his way to vouch for her reputation, Usopp had to do an interview but then it was okay because she made everyone laugh with her hand tricks. The point is Luffy's bond with Robin didn't really develop until Water 7.
Their bond deepened over Sky Piea, but Luffy did state she was a good person the moment the moment he agreed to let her join.
Luffy would not let anyone join just out of obligation.
What a strong bond.
Man, you mock the bond by showing a scene in which they are clearly bonding? WTF?
So, I guess all the times Nami bonks a crewmate on the head, she's just being mean and showing no sign of friendship, uh?
Even Yamato calling Momo "-kun" shows affection.
Yeah I know it's a joke but Yamato's bond is closer to the bond Luffy has with Momo. Do you see Shinobu ever bonking Momo on the head? She has a sort of familial obligation because she sees herself as Momo's dad but like Oden she has the blase attitude of the man who left his own family on an island to keep doing what he wanted lol
You yourself admited there's a bond forming here. You compare it to Luffy/Momo, who have a strong bond, or even how none of the retailers get that close to Momo because they see him as his lord, and compare it to a familial obligation (guess what the crew dynamics are often compared to?).
Avoided it to the point of it being unnatural. Like Oda is saving a big meeting at the end with everyone where Yamato can have a big show off moment.
Okay, maybe it happens next week, but it hasn't happened in 57 chapters. That's longer than a lot of arcs.
You mean the one where Yamato literally states she wants to go out to see and explore the world like her idol? Spent hours reading Oden's journal on all the cool places he went?
This happens there too:
As well as a reframe of Yamato's supposed dream:
What, suddenly going out to the world isn't his ultimate goal, but a means to an end? Interesting…
BONUS: In the following chapter, Kaido is taunting Yamato by saying the samurai will never accept him.
He says that because he wants Yamato to faulter. How many times Kaido said anything against Yamato joining the Straw Hats? Zero.
She had a cool fight against the current major villain of the arc who she held back till Luffy could come back and would have done untold damage had he been allowed to roam free (in the time between Luffy falling off and Yamato picking up the fight, Kaidou almost murdered Kinemon and Momonosuke) and even passed off the fight from a position of dignity having a cool double team up attack with Luffy.
I did point that panel as a step in the direction of joining. But guess what? He's still "Yamao". And Luffy making friends is something that happens in every arc. That panel alone isn't enough to say Yamato has graduated to "nakama" status.
–------ Edit ---------
Now, there's quite a lot more scenes of Yamato and Momonosuke building up mutual respect, i.e. bonding.
And, of course: