No, not with a mentor!
Okay, let's say I took Tilseck and developed him into a pure Fury build.
1. Why do I need machines if there are no Fire Arrows, and the main battle is unlikely to take place in a Castle?
2. The skills Stunning Blow, Devilish Blow, and Reinforcements won't be effective, as they would be if I were playing as Krag; it's better to use Call to Arms.
3. I also think Inspiration is not very useful.
In the end, to get 500 Fury at the beginning of the battle, I have to take half of the skills that are... completely useless. Is it worth it??
If this tactic works, it's only with Krag! And even then, it's a big question!

By the way, if you level up a Ballista with Krag, will Reinforcements trigger after each of its three shots?

Why are you asking if you think you're right? Just play however you want! As for the pure Fury build, let me tell you an example! My friend and I were playing Orc vs. Orc. He also thought, like you, that it's unnecessary, that he could upgrade so many good things, and he got completely crushed, and very badly at that!
Even though his primary skills were higher!
And then he said, "No, forget it, now I understand that nothing can replace it!" Look, we had roughly the same number of Centaurs, around 650 each! He went first, used Lucky Strike, and only did 100 damage, so without Lucky Strike, it was 50! My remaining 550 killed almost all of his without Lucky Strike; that's how Fury saves you!
If the defense is high and there's a lot of Fury (pure Fury), they will complement each other! The damage is so small that it's laughable! When several of your units are killed, but you deal hundreds of damage in return! Have you even tried leveling it up?