For sure, I don't want the takeaway to be 'actually there's no difference between Darvish and Arrieta or Davies', if you need to put money on who will be the most productive then you should put all of it on Darvish. What I'm getting at is that because of the mitigating factors to Darvish's productivity(some of which exist for the others, like age for Arrieta or inconsistency for Williams/Davies), you're dragging down Darvish's likely standard to a level where variance can lead to one of those others matching or eclipsing him, and because you've distributed the risk in multiple players, that chance is non-trivial even if it's not the most likely. To try to say this in a more concise way, if Darvish had an incredible season in 2018 at age 31, you would be way more confident of him setting a higher standard than 3.1 fWAR in the following year because he wouldn't have the age or stamina concerns he has now. Since those concerns do exist for 2021, you create greater surface area for other players to match or exceed his productivity, especially when you have multiple players doing so for the same resources.