Sure, It could be that way.
Overall I think Sengoku's fruit Is one of the strongest there Is, possibly even stronger than the Dragon fruit since Buddha Is, I mean, Buddha, but I don't see Koby fitting well with It.
I don't agree with this. Personally, I think the Kira Kira Is one of the strongest paramecia and with Koby would be a dream fitting.
Koby, after Honesty Impact and all, Is mostly lacking in the defence compartment. Well, the Kira Kira takes care of this better than basically anything can.
The Buddha fruit, or a zoan fruit in general, can augment his resistance, but the Kira Kira would simply turn Koby impervious to almost any damage. And as far as I am concerned, Diamond > Dragon scales in term of toughness.
This was beyond impressive:
By Mihawk, a black blade Saijo user and WSS.
Also, as Luffy G5 was covering himself with Advanced Haki, can you image Diamond covered with Advanced Haki?
Would be basically unkillable, not blows, magma, slashes and so on.
That paired with Koby's CoO.
And the Kira Kira would also boost Koby's offensive: a diamond punch Is way better than a normal punch.
I agree It has no "history", but that Is way imho It would be better: Koby would be the first to really use It and the Kira Kira itself Is incredibly powerful as a fruit, but with Koby specifically, given this increbile fit, It would be a game changer.
Suffice to say for It's power that we thoguht It would be Shiliew's fruit, and so one of Zoro's final adversary. And would have been such precisely because of the fruit.