No! I'm going based off manga fact
Fact is Garra is a long range fight who usually starts off in flight, clone or with a massive sand storm.
e has means to counter or bet yet avoid genjutsu
Itachi hasnt fought against an opponent like him, so you can't assume he start off according neither
You might want to re-rrad the manga, Garra's fights and abilities and see what i mean
Stop it!
so you are assuming Gaara would start the fight in his flight mode? From most of his battles (against Deidara, 4th kazekage, Sasuke etc. )
the very first move Gaara used was trying to cover his opponent with Sand while staying on the ground. #MANGAFACT check for yourself
Now that's important because-
Orochimaru also tried covering Itachi with snake, and he got caught
Deidara tried covering Itachi with clay, and he got caught.
You don't need to be cocky to get caught in Itachi's genjutsu.
Gaara's chances of avoiding genjutsu is very thin if they fight without knowledge.
Now lets see what happens if they fight with knowledge.
That would mean Itachi knows everything about Gaara's ability and he would go Susanoo from the beginning strike Gaara down as soon as the battle starts with a combination of crow clones and all of his power moves before Gaara even gets a chance to move backwards.
Your argument would be valid only if, Gaara has full knowledge on Itachi and Itachi has no knowledge on Gaara.
He can keep distance from itachi using flight and when gaara activates the third eye he covers himself with sand.
Itachi isn't the slowest ninja out there and he could easily close the distance when Gaara tries activating the third eye. If Gaara tried using the round shield he used against Sasuke, that would make him an easy target for totsuka.