Does Koyomi ever get more powerful in the Anime or Light Novels? Looking back on Bakemonogatari and Nisemonogatari, it seems that


   Koyomi is really weak compared to all of the oddities he faces. Suruga's monkey form easily defeats him (even though his power was temporarily boosted). The snakes in Nadeko snake would have killed him had Kanbaru not intervened, he needed to be saved from Black Hanekawa by Shinobu. In the latest episode he would probably have died if Yozuru had decided to prolong the fight. This is in spite of him getting the largest power-up yet from Shinobu.


Considering that he once told his sisters that


  The first requirement of being a hero is to be strong, and the they're fakes given their lack of strength, it seems odd that Koyomi is so underpowered compared to the oddities he faces.


Does he ever get stronger in later episodes or in the Light Novels?
You are wondering how can he can


   tell his sisters that you have to be strong to be a hero despite being rather weak himself.


But does he ever


   claim to be a hero?


I can't recall that he did. Thus, there is no discrepancy in his words and the story he sees in himself is not invalid.

His sisters, however


   did, quite proudly, claim to be heroes. He only (rightfully in his opinion) pointed out that they can't live up to that standard.


On a meta level: Not every story needs a strong hero - many great pieces (commonly for adults) rather tell about the weaknesses of a person rather than their strengths. I would consider Monogatari well fitting in this light.