13yr old Itachi happens to have the strongest visual technique ever introduces to us in the series. If anybody should be being questioned, it's you.
You must be registered for see images
Itachi used one seal to summon the crows, plain and simple. Seals don't magically decrease just because you're skilled at them, sorry. For Itachi's summoning, that's all he requires to use.
Itachi
unlocked the greatest(debatable compared to kamui/ka/limbo/rinne techs etc) techniques. His mastery with them is debate.
What lvl susanno does he have?ribcage? Skeletal?
Does he have the spirit weapons?
How many times can he use it in a day?
You can't answer these questions. Heck his tsukuyomi back then was so bad seven year old no sharingan sasuke remained conscious.
You're using a half empty deck yet expecting a full house.
Edo itachi used one seal. Not 13 year old itachi.
Yes they do.
Example 1:
Zabuza and kakashi needed 44 seals to use a water Dragon
with a pre-existing source of water. Mei did the same with
one seal without a source of water.
Example 2:
Sasuke and kakashi no longer use seals for chidori/raikiri despite it originally requiring 13.
Come with something better bro.