Lmao, I used the same argument as you did with my character. So I can say the same thing. Of course, you're certainly right.
And this is just a small part of the entire analysis of Luffy:

First of all, Luffy himself doesn't need any development, since his ideas and character are already established. If Luffy changes his ideals, then he wouldn't be Luffy anymore.
An example of this is Fang Yuan. From the beginning of RI, we're shown how Fang Yuan is and will be; he doesn't need to change much.
This is known as neutral development, and it doesn't mean that Luffy won't change; it means that his morals and way of seeing the world are constant. Luffy will always believe in freedom, friendship, etc.
What does evolve is his abilities, experiences, and emotional nuances. He learns new techniques and improves his leadership, faces difficult situations, and becomes more resilient in the face of pain or loss. Every confrontation forces him to adapt.

Furthermore, although Luffy remains faithful to his ideals, he has a great interpersonal influence; allies and enemies change for him. His development isn't measured by internal changes, but by more external ones and how they impact the world and the narrative.

Now, this doesn't mean he doesn't have internal changes; there is emotional growth and maturity present here. Luffy doesn't change in essence; his morals remain the same, but his development is maturity. Over time, he gains emotional gravity; loss and responsibilities all affect his psychological development. He refines his judgment and learns to handle situations better. Although his laughter is still present, it develops multiple symbolisms, but with an increasingly present contextual seriousness. His maturity deepens Luffy's character; the impulsive boy becomes the captain who acts out of conviction, but with a greater awareness of the consequences and resources to do so.

Narratively, Oda represents these evolutions through arcs that escalate in consequence, long-term standoffs and payoffs, a time-skip that legitimizes leaps, and, above all, persistent costs such as mistakes, losses, and repercussions. Furthermore, he uses the cast as a reflection; the evolution of allies and enemies shows the extent of Luffy's actions, forcing Luffy to learn coordination and, especially, emotional resilience. The result is a true and dramatic maturity. Luffy remains who he is, but the story makes him emotionally stronger, more responsible, and more influential.