2Server
Despite all these interesting calculations, I'd like to add my two cents...
I understand that the speed is calculated as an average overall speed, but in a real battle, the hero with the fastest creature will move first. For example, Valeska with angels will move after the Swamp hero with upgraded dragonflies. Consequently, the right to cast magic first will be on the side of the Swamp. And if this hero is also Tazar (around level 20), then... the whole "gradation" can go out the window.
+ In addition, it is necessary to take into account that after a massive speed boost, there is often a massive speed reduction in response, which "levels the playing field."
And judging by: "at high levels, running off the battlefield with all the artifacts... gets boring...", this "gradation" was more intended for playing against the computer. Isn't that right?

I just can't bring myself to call Inferno strong, and Swamp and Necropolis weak...

But to each their own, it was interesting to read...