I can and I did.
Gai is strong but he's not legendary, the way Gai made the sound nin pass through a wall during the war was impressive.
But it's nothing compared to what Tsunade did without even seeming to force herself when she destroyed a street with a mere kick or worse when she swung Gamabunta's sword.
In term of Taijutsu and speed Gai seems
way better than Tsunade but in term of pure raw physical strength they just don't play in the same category.
Yes it would be the better choice because like I said against a Sharingan user such as Itachi usual Ninjutsu and Genjutsu are basically almost useless (I insist on 'usual', I don't speak of a Kage level fight).
But I don't see how it could be enough and by far.
Does Gai would do better against Itachi than Kakashi?
I don't really know, he has the ability to avoid the genjutsu effect of the Sharingan but at the opposite of Kakashi he hasn't the same insight to avoid the more regular jutsu of Itachi (and i don't speak of the Amaterasu given that we still wait to know how it works).
Here the point, Gai is a Taijutsu specialist, Itachi can beat him in no-time very easily, why?
A simple use of his explosive Kage Bunshin. Everybody is impressed by the Tsukiyomi but this jutsu is overkill as well, Gai who fight in close combat would be in huge trouble because of this jutsu.
Without speaking that against the level of Sharingan of Itachi, being simply faster than him wouldn't help at all.
So in the end does Gai would do better than Kakashi, I think so because in the end Kakashi was crushed extremely quickly.
But much longer and during a way more difficult fight?
Frankly I don't think so, as I said even with the very few moves that we saw from Itachi Gai would be seriously in trouble.