So I was curious and looked at the tool tip on the same character on the same weapon bar and I noticed that at the max execute range, these abilities do the same max damage, yet Whirling blades does a higher minimum not accounting for passives.
Whirling blades is more expensive but then you account for Ruffian and it makes it 20% more damage.
Add in the reverse slice does splash damage of only a fraction and whirling blades does full execute damage with the greater minimum damage to the targets around. Which you can argue situationally, there will be major evasion up but then we can also say Slaugher takes up 20% of that, plus we need to account for dual wield having slightly more built in damage natively. You could also then argue situationally also being minor evasion (only one source of that I know of) but then I would also suggest Ruffian well outpaces that and is much more likely.
Then; even post nerf/swap of execute ability and spammable to where the execute is on a shorter range; it is still 6 meters while Reverse Slice is 5 and Whirling blades does not need the target to stay on your side of another enemy due to it being targetless.
Guess what I am saying is the patch has not changed anything. Whirling Blades is the choice execute in practicality and strength