Currently on stack chart when hovering on an area it only shows the values of the what the mouse is hovering on, it requires the users to be more accurate with their mouse hovering, which in busy charts can be challenging, also it is harder to compare values since you can only get a single value at each time. It will be more helpful if in stack chart you can see the values of all the stacked lines/bar/areas once hovering, either in the legend or in the tooltip (preferred)
current (you can't tell how much exactly the blue bar is):

multiple values in tooltip: