@Robby:
That's exactly what Oda did tho. Everything with Haki is a brand new move set to let Luffy do things rubber powers alone couldn't do, like knock out giant crowds with a glare, hit Logias, make his body iron hard, sense people at a distance, or see the future.
Even without that, you have the gears. Which you can psuedo justify under "rubber used in a creative way" but giving Luffy super speed and smoke in gear 2, giant limbs in gear 3, flying abilities in gear 4? Extrapolations from rubber maybe, but nowhere near the original design intention and typically powersets unto themselves.
Then you get things like Red Hawk where luffy can make fire? Or talk to and understand animals? Or one off anomalies like Water Luffy, giant gold ball Luffy, Nightmare Luffy, where he gets a one time powerup that lets him do things he doesn't normally do. It's written organically into the story or provided by an outside source, but its still a power he got that he didn't have before or use since.
Luffy hasn't just been a "creative rubber user" where his powerset includes "stretching" and "bullet immunity" in a very long time.
ANd this extends to the other main characters, especially the likes of Brook and Usopp who have completely different powersets post timeskip than they did before it. or Sanji who just got a super power sentai suit that lets him turn invisible?
Their stuff may still fit in a theme, but they've absolutely been getting completely new powers along the way.
You make some good and valid points.
However, when it comes to Haki, Luffy is not the only one who can use it. Instead Oda has made it so that even Luffy's enemies can utilize the same style. Comparatively, Deku is the only one who can do shadow whips.
Furthermore, at least Oda tries to remain in the realm of logic(in the One Piece World) when he gives Luffy, non-rubber related powers. For example, its very plausible to believe that someone who is made of rubber, can artificially increase the rate of blood flow throughout his body. It maintains internal logical consistency.
The one off Anomalities were instances of Luffy actively making use of the environment to beat an enemy he couldn't beat, so to speak. For example, water luffy is a stupidly reasonable power that makes use of Luffy's rubber ability by holding more water in his body.
I never liked Nightmare Luffy, so i won't defend it.
Luffy's Red Hawk can be explained as Luffy vulcanizing his fist and as a result it releases heat and fire.
My overall point is that Oda has always tried to make Luffy's new abilities fit into the mold of Rubber powers(Not realistically logical but in-world logical) and in the case of Haki, he leveled the playing field by giving everyone Haki and even making some of them better users than Luffy.
In contrast Deku just unlocked a completely new power that has nothing to do with the original and is in no way, shape or form similar to the original. And now he will unlock 7 more completely unique powers. All the author has to do is play around with those powers and let them conveniently get Deku out of tight spots.
I used to think part of Deku's journey would be to develop his own unique way of using Super strength where his natural tactical mind would be used to use the power in creative ways. Now I highly doubt that will happen.
I think a better author would have found a way to expand on Deku's power while still keeping it in the enhancer role.
