[Erosennin900]

Kakashi is the strongest hes ever been, He seems weak because his mangekyou sharingan puts him in hospital everytime he uses it. This is because he has less chakra than other Jounins on his level, and his sharingan uses more chakra because he has a non-Uchiha body.

Other characters have developed which makes Kakashi seem weaker even though he is probably the most powerful Jounin in Konoha, remember he was an Anbu captain at a very young age.

A couple of things to consider:

Spoiler for Manga readers:

In his upcoming fight against Kakuzu, Kakashi shows just how strong he is by destroying two of Kakuzu's hearts

Spoiler for Manga readers:

There will soon be an arc in the manga focusing on Kakashi's/Sakura's development. This will show how strong Kakashi is.