I interpret it as the author affirming the readers that Itachi is stratospheres >>>>> MS Obito.
Itachi possesses immaculate illusory skills, spiritual tools, and an overall fundamentally better skillset, and physical strats. To be specific, his speed is grossly undermined when he could acclimate the features extrapolated below; not to mention the fact that an exorbitant skill degree in casting illusions implicits that this incarnation of Obito, stands absolutely no chance against Itachi, like literally none. The exact reason why this would be case is that illusory abilities are spiritual, the latter can't really ghost phase through them, which is probably why he chronically feared a hypothetical bout with MS Itachi—not to mention the spirit items that he has under his belt, something that's intrinsically linked to his illusory abilities technically — therein, it could be extrapolated that he wouldn't bypass such spiritual items with Kāmui.
Obito consigning Pēin to pillage the Leaf only after Itachi's death (ie., Obito concretely knew that Itachi planned to orchestrate the fight between him, and Sasuke Uchiha, than meet his Maker in that battle simulation like implicited by his back & forth with Sasuke Uchiha in that hideout), and failing to trounce the strongest village on the earth; ie., the Leaf, for straight 18 years implies that there is definitively an entity who pulled the strings beneath the surface area, and that is definitively Itachi Uchiha like exemplified by his inferiority statements, and concrete physical implications. If he was truly stronger than Itachi, then he wouldn't have needed to wait it out for such a long ass time. On the flip-side however — the latter not actively exchanging in an extended bout with the former can be rationalized as him not feeling like doin' it—as the author consistently alludes to the fact that Itachi didn't like fighting, and that he was an innate pacifist who got traumatized by the cycle of warfare that was rampant on earth from the time that he was a little child.
This doesn't apply to Obito; however, as he had every intention to make the Gedø Mazóu eat the Jinchūūriki Chakras to transfigurate a Watered Down Jūūbi like exemplified in the War Arc.
Itachi has a near infinite ways to kill MS Obito.
- HQ 80,000 Fourth World War Shinobi Alliance Acolytes' Puppet Mind Controlling Exorbitant Illusory Skills
- The Sword Of Totsuka + Mirror Of Yata
- Explosive Tricky Chakra Bunshins; that not even Elite Dójūtsu Applicants like 3T Kakashi couldn't perceptively penetrate.
- MS Techniques like Tsókóyomi and Amaterasu (which cannonically exterminated him from the scene — ie., required a most powerful illusory spell like Izānagi to bypass — striking the fact that Itachi himself utilizing that ability would be stratospheres more powerful by virtue of the whole "An Experienced Castor >>>>> A Novice" line of logicality.
- Magnificent Immaculate Speed Features that exceeds anything Jūūbi Jinchūuriki Obito has accomplished in this series, let alone MS Obito.
- Supplementally — a key fact that is often overlooked is that Obito can only spiritualize the part of his body that is preconceived to be stricken with an offensive attack — IE., he can't warp the entire physique if he wants to acclimate offensive damage on the enemy which implies that Itachi can twirl kunais and shurikens in his blind spots to to take him off-guard like he accomplished against a Quasi Prime ET Nagato; whom Obito admitted inferiority to—on 2 different occasions.
Even characters like Hashirama are susceptible to such supplemental damage — Therein; arguably, Obito doesn't fare any better in this battle simulation hypothetically.
