The strongest hero.

As far as I remember, Kha-Belekh has a similar specialization in initiative.
And in general, here they are discussing strength not based on the game, but based on the plot, so it doesn't matter.

I meant that Railag, who simultaneously slows down enemies and speeds up allies.

And if we are talking purely about the plot, then Zehir should be mentioned. He fully participated in 2 campaigns, managed to defeat Markel and the Overlord, and did many other things.