What do you need weapons for if you have tools that are not swords nor bows that can slice anything (except spirit-characters) in one fell swoop?!

Even the hammer can block attacks...
I think you kinda missed the point.

The implication was that the apprentice who likes weapons could make spirit armaments just like how MC made spirit armour.
MC might not need weapons as his Isekai´d tools are better than most, if not all, weapons.
So i don't disagree with you there

But his apprentice does have some uses for it, and clearly wants to learn.
So unless MC can ( and want too ) give some of the tools away having a weapon as a sidearm is not a bad idea.
Even if the spirit magics are faaaaaaaaaaar more deadly.