Rockamush bleed effect not stacking

Bleed effects are meant to stack, but if you use Rockamush’s skill and then a regular piece inflicts ‘bleed’ from the barbarian talent the effect doesn’t stack, it is replaced, which makes it better NOT to upgrade its talent grid as you could undo your own attack.

Bleed effect should stack, no wonder nobody uses bleed heroes

I am not sure that is the case here, but did you check the bleed duration?
If you hit with a low damage/high duration bleed after first hitting with a high damage/short duration, the stacking works out to reduce damage per turn, but the total damage is the addition of both, but spread out over more turns…