i don't know what dark hero days did in relation to the rest. this is just north america.
probably the only two in the series that were disappointing were d4 ps vita, especially considering how d3 did on vita, and dd2 compared to the expectations of a direct sequel to disgaea 1.
Was Disgaea 4 Vita significantly lower then? Assumed it hadn't done that badly since it was just one ranking below Disgaea 3 Vita. Interestingly did better in Japan, at least opening week (probably will get a similar LTD with the budget re-release).
DD2 came too late in PS3's life imo.