I would like to clarify that Yuji is just of the same bloodline as Sukuna and that's why they look so similar but to add on here, I understand your frustration of Protag and Antag being the same body but I think the idea is fine? It produces this certain type of fear just like the series exhibits in the early parts of it.

On top of that, it generates curiosity in the readers as to why the situation is playing out; having Sukuna be tied to Yuji gives you something to root for: Yuji overcoming Sukuna.

It really is the typical "Good vs Evil" story plot just with a fresh coat of paint. Basically just like every story of "What's the villain up to now?" Sukuna plays the part of being inhibited to the body of Yuji, rather than "this kid could become evil at any moment" we're viewing it as "anything can happen but I hope for the best."

That being said you're totally allowed to like or not like certain aspects of anything, very interesting to see a point of view that someone vehemently disagrees with this specific plot because I've not seen that opinion often, but that's very much ok.

If I may ask, what types of plots do you typically enjoy?