Kishimoto gave Itachi this godlike and invincible appearance duo to his attitude.
We've seen alot of battles in Naruto by now and we've seen that every character in Naruto atleast once rushed into battle too fast and underrestimated his opponent.
Itachi has never shown that he underrestimated his opponents and never rushed into battle. He praised his opponents when they did something unexpected, yet stayed calm, focused and analyzed the situation. Itachi ironically enough was the one who said that ''Every strong opponent has its weaknesses'' and ''Every jutsu has a weakness'' the reason to why Kishimoto gave these lines to Itachi is because Itachi had the right attitude. Itachi said that you have to analyze the situation before you act and this is why Itachi was able to end battles in no time without ever showing his real strength because he never intended to kill his ''friends'' as he was one of the good guys. Itachi has also shown us that he is able to use his tools and jutsu's very effectively and has shown us that he was able to use and control his low chakra reserves to the maximum as he was able to keep up with Sasuke (even surprised Sasuke with the fact that Itachi was able to pop out Sasuno'o with no chakra). This too shows how conscious Itachi was with himself and the situation around him. There's a saying that says: ''If you're not stronger, you have to be wiser'' and Itachi has shown us that this is indeed a fact.
Also Itachi's wisdom and intelligence is unmatched, he has the best quotes in Naruto. Nice examples of Itachi's wisdom are his conversations with Kisame (when they first met in Akatsuki), Naruto and Kabuto.
People can hate Itachi all they want but for me Itachi has shown that he's able to take on anyone in a 1v1 duo to the fact that he's the right opponent with his intelligence against characters who's raw power are over the top.
''Those who are strong become arrogant'' is a quote by Itachi and arrogance leads to being unable to think clearly which leads to making mistakes and these are facts, and making mistakes against someone as calm and observative as Itachi leads to hell.
Itachi haters gonna hate. Go suck on this thread.