Yes, but you missed the point, it's not the process, it's the result. Sanji (the end result) doesn't have "abilities/power" like his brothers. That's why his brothers are modified human and the weak ass Sanji is just a human. He left germa as normal human (the classification he belongs to).
If Franky failed to modify his body and became a cripple with no addition whatsoever, would you call him a cyborg?
We can take a look from another perspective too about this topic.
East Blue recruits : 2 top tier strength, 2 low tier strength
Paradise recruits : 4 mid tier strength
New World recruits : 1 top tier strength (Jinbe), 1 low tier strength (Carrot)
This can change, but it's more balanced this way. It feels off if we get Jinbe and then someone stronger than Jinbe (Yamato). She will overshadow him and that's bad, especially since Jinbe 10 years buildup vs Yamato 10 months buildup.
Sanji is just yet to unlock his exoskeleton... But it's there... Still modified...
I won't call Franky a cyborg if that's the case... But he's still modified...
It's just as simple as having a failed surgery IRL, still surgically modified, just with failed results...
Do you seriously think Jinbe would be overshadowed by Yamato? Did Sanji overshadowed Zoro when he joined? Did Jinbe overshadowed Zoro and Sanji when he joined? Not that I'm saying that the new one is more powerful than the other but the thing is, you said it, 10 year buildup, only to be overshadowed? Besides, we don't know how powerful Yamato really is to conclude that she's more powerful than Jinbe... She drew with Ace and fought Kaido multiple times, that's all we know... For all we know, Oda likes to nerf female characters, Robin is a prime example... At most, I can see her power just a step inferior than RS Sanji and Berserk Jinbe...
There's just simply no room for another weak tier in the crew which would be facing Yonkos and WG top fighters one after another...
So is Jinbe.
Yamato be overlapping with the oni theme, and she doesn't have much else going for her, therefore it's easy to see her character creation was never thought of to be one of the strawhats.
Interesting... Like Carrot (or any other mink) is to Chopper... Even their best forms are quite similar and overlapping...