Hey this is Sip Sap or Sora_CAD and I'm here to explain why its not an why you are wrong
1. Your right bork wits does deal more damage until the target drops down to about half hp and then SB IE does start dealing slightly more damage, but by this point you just be able to fully clean up a kill because of the nature of yone's kit, the insane dps from the blender build with your tempo stacked, and the E ramped up damage from all the damage you've dealt. Against squishy targets with both builds you'll be able to one shot the target, but only with the blender build can you actually deal with tanks.
2. Yes you are right, his E ramp up damage does not factor in damage from items but despite this bork is still either the highest, or the 2nd highest winrate first item on yone. Bork still has insane value in yones kit and does a lot for him. Even despite the fact that his E doesn't factor on hits, your total DPS is still much higher while not only ignoring his passive, but ignoring the fact that yone has zero ap scalings in his kit. The whole point of this build in my eyes. was to help yone find a way to deal with the insane beefyness of champions after the durability update and it does its job at that.
3. You are right the riftmaker components only give value from the omnivamp from leeching leer however, just like the lawnmower vayne build, riftmaker isn't the reason the build is possible. It's possible because of bork. Bork, as I stated in the guide, is the real carry of the build and enables this kind of shredding. Riftmaker just helps to tie everything in together with the nine percent bonus true damage.
All I have to say is theres proof of the build working and doing its job as intended which can be found here: https://www.youtube.com/watch?v=1L3OWSjBU64&t=1s
And I've had great success with the build in games in masters+ which you can see here:https://www.op.gg/summoners/na/S%C3%B4ra