Does a natural 5star unit have more attack than a unlocked potential one?

So as many others I too have gained enough feathers for my first 5 star unlock, I've run into a problem tho.
As far as stats can tell, any unit I'd like to improve has a too low attack value when compared to that on the IV calculator, all the other stats are correct tho.
Example: Corrin(F) should be at AT LEAST 20 attack, but mine would be at 17 as 5star lvl 1.
I hope someone knows anything about it, tnx