I think the real question is, was he always sick? ( ͡° ͜ʖ ͡°)
Was his chakra always low or was it after he got sick?
Itachi’s chakra is low yet Hebi Sasuke ran out of chakra before Itachi did, and this is the same Hebi Sasuke that outlasted Deidara in their fight.
When we all stop confusing stamina(physical energy) with chakra then we would all know that Itachi never had low chakra. You can’t have low chakra and use the mangekyo sharingan. It’s impossible.
Sasuke only ran out first because he intentionally use up all his remaining chakra for a fire jutsu to set up Kirin. If sasuke wanted to play the chakra conservation game he would've out lasted him.
Deathbed itachi had better chakra and stamina than curse mode Sasuke.
Was his chakra always low or was it after he got sick?
Based off what? Did you forget that Itachi used two crow clones against Sasuke and then used a genjutsu and a crow clone against Naruto before their final battle at the hideout?
Itachi wasn’t conserving chakra, he was dumping it out just as much as Hebi Sasuke did and Itachi last the longest.
He used Amaterasu and Susano’o, when Sasuke did that at the summit he ran out of chakra and Zetsu had to replenish him.
Stamina! You can literally post the databook yourself. And again he used genjutsu and 3 of those clones before his fight with Sasuke. Chakra has already been spentyes. 3ms usage was always his safe limit. And the moment he went past it he died.
crow closes use less chakra though. They are designed to save. -_-