Warcraft III - fps drop

Hey,

Let’s start with this:

https://i.imgur.com/oWg8Uza.png

GPU usage - 16%, CPU usage (2 cores) - around 50%, fps - 20. This kind of fps drop, with low/medium CPU/GPU usage, happens to me every time when there’s a lot of units/hp bars on the screen. Is this a game engine that doesn’t know how to use more power from my PC? Or the problem is elsewhere?

Spec: i5-5675C, GTX 970, 8GB RAM, Windows 7. Everything’s updated etc.

I’d be grateful for some help.