Thats why i also wrote draw. and you used nagato when you meant itachi. But, an healthy itachi and healthy nagato would have been just like how they were when they was edos.I suppose you mean a healthy nagato vs a healthy itachi.
To state the obvious first. Even if nagato is healthy he still lacks mobility as we saw in the manga. Due to not being able to walk for more than half his life. Clearly speed goes to itachi.
Could argue that the reason itachi's stamina stat is 2.5/5 is due to his illness, therefore he should have the same chakra level as sasuke 3.5/5, therefore its safe to assume that a healthy itachi would have a similar chakra rating as his little brother.
A nagato that lacks mobility is vulnerable to several attacks although granted he has counters for everything, apart from the totsuka sword. If nagato was to stand stationary and attack, he wouldnt prevail.
What i will finally say is that nagato himself lacks combat experience fighting as nagato. Since he lost his legs from a young age he as relied on dead bodies to fight for him therefore he hasnt really exprienced a real battle fighting as nagato. He hasnt been in a life and death situation fighting as nagato. When we did see him fighting as nagato its clearly showed that he is inexperienced. His battle with hanzo and co but also itachi, bee and naruto confirmed this.
Against itachi raw power alone wouldnt win you this. Imo it can go either, best chances itachi has is to end it before nagato decides to use ct
If we go by how they were when they were living both wasnt healthy, but we both know itachi would last longer being edo than if he was living. with his stamnia as 2/5 and naruto being an uzamaki he should also have a 5 but i'll wait for the data books. It can go either way, who ever seals who first basically.
The genjutsu thing, idk if itachi would be able to find the real nagato if he is able to kill all his bodies which with his stamina i doubt it.