He mentions a number of things, including "You had many things that made yourself". This implies he did indeed envy Itachi for who he was, not purely strength. Or rather, what made Itachi special is that he had strength that he developed and could call his own. Madara is stronger, but also had EMS (a power entrusted by his brother) and Hashirama cells (a power stolen from his rival). Furthermore, he treated Madara more as a science experiment. On the contrary, his mannerisms and praise towards Itachi are completely unlike how he talks about Nagato or Madara, despite both being unambiguously stronger than Edotachi.

What mannerisms and praise are different exactly? If anything, he says it in a different tone, as if he reiterates the kind of hype he gave Nagato, in a more respectful manner to Itachi.

Your first example clearly points to the amount of power, Itachi build up throughout his career. Why'd he envy someone else if not for power and for ideology? Especially when all he cared for was power and power only? He bluntly voices his opinion on how he doesn't wanna hear Itachi's lectures but rather want the power he possesses.

It was never hinted that he praised Itachi because he made himself without requiring outside power. He blatantly makes a broad statement in reference to all of his Edo Tensei, and calls him the best.

That has to do with Itachi's brain too. Mentally he is not like the others.. he can and will figure out his opponent and opponents techs extremely quickly and defeat them. He figured out near instantly that the Rinnegan Summons were all linked in vision with Nagato himself and he flawlessly, from blind spots, blinded all the Summons eye balls. Itachi isn't dangerous because of raw power or chakra reserves and dbz explosions like some characters lmaoo.. but he is very dangerous because of his projectile weapon skill, hand speed, sharingan mastery and his brain.

How can Nagato, master Rinnegan user, be weaker than Itachi? Even Edo-Tensei old, fragile Nagato would beat prime Itachi without breaking a sweat. Nagato is the second strongest Edo Tensei. No debate needed.

Except he did, as i quoted, as referenced in chapter 585.

Think of it this way. Itachi, in a hypothetical fight versus Sage Mode Jiraiya, would probably lose. Six Paths of Pain just curb-stomped Jiraiya and Nagato by himself is stronger than his 6-man corpse army.

It's not clear whether that was what he was implying.

He bluntly voices his opinion on how he doesn't wanna hear Itachi's lectures but rather wants the power he possesses.

Clearly insinuating he wants just his power.

old edo tensei, "immobile" nagato would get one shotted by totsuka blade as per canon. He can't mentally react to the blade as per canon to even use shinra tensei lol, so good luck to him improving his reaction time. Kabuto was referring to itachi's strategic mind and power. Itachi is a genius of combat, not a whole lot of shinobi can read the opponent's patterns of attack, break them down, and counter them as well he can, while also having MS hax at their disposal. kabuto wanted itachi's mind and powers. Nagato has more raw power but that's it.

Nagato was under mind control for that fight, so that was just Kabuto using his Body and its techs, Shit Kabuto didn't even try to use the massive Shinra Tensei and he just had Nagato standing there looking dumb while the smoke was clearing.. so that't not a fair comparison for Nagato fighting style wise.

@FlatZone

Ok, so Kabuto couldn't mentally react to blade then. But you would have to assume that Nagato's own reactions are significantly better than oro's or kabuto's. Orochimaru also didn't mentally react to the blade until it pierced him. Also, nagato was standing a fair distance away from the smoke, we have seen him reacting to rasenshurikens coming out of smoke screens, and in this case the smoke already was clearing when itachi launched the blade. That should have been plenty of time to react. I don't think it was that nagato was standing looking dumb, it's standard to wait for smoke screens to clear before reengaging. Jiraiya also stood there while the smokescreen from his goemon was clearing. so kabuto/nagato couldn't react to the blade. We have seen Pain himself walking through smokescreens without using shinra tensei (such as vs kakashi), so that wasn't OOC. I think it's safe to say that people hyped for their reflexes (Ay, minato, sage users, and above) would be able to dodge the blade if they see it coming head -on without a diversion, but I doubt Nagato fits that category.