A champion like Ahri is balanced around having 3 dashes with her Kit
But when Sylas steals her Ult , not only he gets 3 dashes ( with the 2 dashes he already has ) , his Ult ( the Stolen Ahri Ult ) deals more damage than Ahri's ult despite having more AP than him.
It sucks picking Ahri into Sylas then he does more damage than you with your own Ult while watching him dashing around then proc his passive freely for every dash
Not only Ahri tho , the same goes for other Ultimates that don't deal much dmg , maybe like Shaco's Ult Clone explosion? not sure about the numbers , can't think of other examples but Ahri's Ult is the best Example .