Yawg as a litmus test of Control vs Combo Oath builds
I play a lot of Oath, and ran Yawg for a long time, for many of the same reasons listed here. (Obviously, since its a really powerful card and can just win the game when both players are just in top-deck-mode.) But I dropped it last summer for a Show and Tell. (Full disclosure, I'm running a much more controlly version of Oath with Standstill, with a huge density of counterspells.) The reason I finally dropped it, was that I found that in a lot of games, the reason I was in topdeck mode to begin with, was because the opponent had already landed a Cage, taking me off the main win condition for the time being. In those cases Yawg is really bad. So after some testing I just did a calculation, are there more games where I win because I found Will, when I wouldn't have won otherwise... or are there more games where I'm losing when I find Will, and I'm losing in such a way that Will is bad and doesn't help.
For my deck, I calculated straight up that there were more games of the second kind, mainly because Oath is just so strong and consistent that if the opponent doesn't do something to either lock you down or kill you, then you probably just kill them. With the build I run, that can also mean just getting rediculously far ahead in cards. (Any deck running blue anything can win that way, but the point here is that more control Oath decks, with more card drawing and higher counter density actually do it with frequency, as a main strategy.) I also noticed that the bulk of the games I lost involved 1 of 2 paths to defeat, either the deck just killed me with some insane broken opener (Storm or Dredge)... or the deck locked me out hard in the first couple turns (Shops mainly, or sometimes Hatebear or some Gush variant running Cage or Priest). In the vast majority of those games I lost, Yawg would not have helped. In many cases it would have been totally dead due to Cage, or Sphere effects (even 1 can make it pretty useless), or because I was just dead and scooping up my cards to Storm or to Dredge that ripped my hand to pieces. I really didn't see that many games where I felt like Yawg would have made a big difference.
(Now there are certainly games where you do get to show off your Yawg. Usually this is Oathing into a Griselbrand and drawing a ton of cards and Time Walking and then Yawging back the Time Walk and just blowing some dude totally away, but I ultimately decided that while being able to do that was convenient, I would have won the vast majority of those games anyway, either by Oathing a second time (I only run 1 Gris and other creatures, so no worries about legends rule), or just drawing a bunch of cards and counterspelling the whole world until I beat the guy to death over a couple turns. Obviously there I times when I would have killed someone outright with Yawg, and then they barely kill me with something else because I let them untap, but honestly, those are really really rare. (We think they are a lot more common than they actually are... because this it plane crash psychology. We perceive that flying is more dangerous than driving because when it goes wrong it goes spectacularly wrong so it sticks in our minds.) I found that for my build, the value of Show and Tell being blue and making big creatures in my hand be live, outvalued the power of Yawg. Also, I run Cruise, and Cruise is not friends with Yawg, but is friends with Force of Will.
I am not saying, that Yawg is bad or shouldn't be included. If you are running an Oath build that is a "combo deck with control elements" then yes, I would think Yawg would be great. Because really what you want to do is just slam threats and blow the other guy off the side of the world as fast and hard as you can (A really good strategy. I really mean that too. Just be the first guy to punch the other guy in the face, is a really good way to win vintage magic games). For those decks that are running 4 Oaths, and multiple Show and Tell, and Gris into a ton of cards to try to kill before they untap, Yawg is awesome. My read is that as there are more and more control elements introduced to Oath, Yawg gets worse and worse and worse until the point where it should be cut for something that is at least blue. So really, I think the question is, where do you fall on the continuum between speed and control. Since this is the Fenton Oath thread, I would think that Yawg is probably an include in most of these builds. But I really encourage Oath players to count games they win and lose, and do postmortems on how those things happened. Just because you played Yawg and won, doesn't mean you won because you played Yawg. And if you lost, would Yawg have changed that, and by how much percent. If you are asking those questions, good choices are going to get made about deck construction.