This reminds me of a SCP entry where the SCP Foundation couldn't contain a Keter entity that was a little girl if she knew of her full reality warping potential. In order to keep her under their control the SCP Foundation gave the girl a made up story of her being some witch that can only utilize a select few powers so she herself can limit her own powers.
So what if Shanks immediately came up with the Gomu Gomu No Mi and it's properties so that kid Luffy limits himself and think that the stretching of his limbs was just the results of the Gomu Gomu No Mi and nothing more?
So what if Shanks immediately came up with the Gomu Gomu No Mi and it's properties so that kid Luffy limits himself and think that the stretching of his limbs was just the results of the Gomu Gomu No Mi and nothing more?