One of the first witches he meets is named Wendy and control Wind (wendy /wind see what you did there Author). For, like 840 chapters, NOT ONCE he thinks " Hey! maybe she doesn't control wind but gas ? Could be Handy if she could, I don't know separate oxigen and Azote and other gas in the air to get the chemical elements I need to make bomb and stuff ".
To make it simpler : He thinks with his knowledge not his brain. There are many witches whose power is under-used and developed just because it doesn't fit his knowledge.
Another example : Nightingale. Her first power is turning herself invisible, but not like the invisible man where she needs to be naked, all her clothes and equipement turn invisible too. AND NOT ONCE did he think " if she can turn her clothes invisible maybe she can turn other things or people invisible too".
So much possibilities and yet nothing. It's depressing.)
Hell, when the prince almost died taking a shot aimed at Anna, the story is focused on Nightingale and what she's feeling at the moment ! Anna ? we got two lines where she tells about her feelings and it's 2-3 chapters later !
About 600+ chapters (and a "will you marry me?" between Anna and MC around chapter 400+), MC before Nightingale's heartbroken state for failling again to protect him (funny, everytime it's not her fault) decide to throw her a bone. Short story short he will talk to Anna about her, and she will need Anna permission to be romantically involved with MC.
It's around 880 now and still nothing... just more about her in the MC interacting and a few scenes with Anna.
It's damn frustrating.
When she said that starting from level 5 pharmacology begin to be really difficult to improve, MC look at her, then put 5 points in the skill making it level 10. Infuriating the elf (What an A-hole...)