Teinen-go wa Isekai de Taneuma Seikatsu - Ch. 9

[SifTheFair]

Those are very situational and might not be worth training a high ranking officer nor staking your whole strategy on a single person. In other cases you would have to cast those in the timespan it takes you to be instagibbed by a fire spell, and you still have to sustain for longer to strangle someone.

I mean we can argue over it, "standard" offensive magic like fire, lightning and probably rock spears, should be already expected and maybe even planned around.
Impeding your army, be it by making the ground a marsh or just by throwing water at the soldier would require more than just a "counterspell".

Even then, and let's say they don't want to bother to train magicians for that, high pressure water spell shouldn't be "new", because water spells could just be a mimic of other offensive spells.

In the end, it's the fault of the author to not give a credible reason for them not using water magic, it makes everyone reflect poorly : the mother, the sister, the army and the research group.

 

[Amenohi]

Many might not realise this, but it takes precision engineering to get a water jet cutter. Just look at how long it took from Archimedes to the first water cutter. Just the idea itself is rather hard to grasp. The thing they might come up is probably dependant on volume.

Though if there is one thing strange, it's the fact that water is considered weakest. No way is it actually weaker than wind. An incompressible fluid has got to be more powerful than a compressible one in combat.

 

[VooXoo]

I approve MC introducing water pressure cutting, but in a world with magic and research for no one to realize its war ability is...stupid.
I even dislike how a simple direction made her able to make a water slash, a better way to put it in would have been MC explaining it to her, she doing some attempts, OUTSIDE THE HOUSE because a laser cutter would go through walls and people alike, she failing, MC helping her to make the pressure right until she is able to do it after half a day or a week.
As it is MC introduced a skill anyone can replicate on the spot.