Great you ask! First, Striker got so good at widow in really little time, able to contest and Even defeat at times in the play offs. Widowmaker is a very complex hero that requires a Lot of concentration and Focus on the game, which Add provides. Players like surefour got so good at widow because they are hitscan mains, but striker before playing widow he only played tracer, junkrat,and a little phara. Remember what hapened to the BU internally in season 1, maybe he used it to increase his skill and keep his spot. Great player Tho.
Fleta probably does not use it but is curious the fact that he was really incosistent and maybe ir could be that. This is my opinion, thanks for asking!