It is hard to tell if it’s working at all because the damage looks like whirlwind damage. Rend puts the red marker on mobs and they melt. This just looks like another hit. It also did not appear to take any rend runes if you had the skill rend on your bar.
I would increase the damage and slow it down to 3-5 seconds
It does use the rend rune you have on your bar. It’s also doing all of the damage now.
The point of the Ambo skill power is to reduce server calculations and server lag. So I don’t see them extending the duration.
It’s best to not look at it as Rend, but just a different form of Whirlwind. Because technically it is just your Whirlwind.