@SNIper-poTAto The cardio would be broke, people would put DR on it and start runing and never stop...I would be like playing against a raum that has unlimited dash.
The only reason people pick burst is because of the damage... If you reduce the damage you might as well remove the talent.
Removing the ability to head shot would be ok idea.
I do like the nade idea though, it destoys your ability to bounce the nade. Maybe a combo. Nades work normally but exlode instanly on direct hits with players only