I get the feeling you didn't read my comment, I understand it was long, but you should in such a discussion.
High 6-A Scaling
Base Yhwach:
You bringing up calcs for Bankai Yamamoto indicates you did not read my comment as I said verbatim:
If you read through that thread, it was actually SoldierBlue, BurningFullFingers and Dark649 that stated Bankai Yamamoto, Dangai Ichigo and Hogyoku Aizen as all superior to Shikai Kenpachi. Which reinforces the High 6-A Base Yhwach as he is above Bankai Yamamoto.
Yamamoto was labeled High 6-A not through his own calc, but through Shikai Kenpachi. I layed it out clearly to not leave holes.
As for directly scaling to Gremmy, Yhwach sealed Gremmy away:
While the war with the Shinigami was in full swing, something else was going on within Silbern. There had previously been a cage; heavily sealed by a barrier set up by Yhwach. Now, however, the seal had been unraveled and the existence that should have been locked up was revealed. The body of Gremmy Thomeaux was standing in the passageway. Nobody approached him, nobody even dared to look at him; as if fearful that just by looking into his eyes, they would get killed.
Need I also add, Yhwach gave Gremmy his powers.
True Shikai Ichigo:
I am unsure why you're bringing up your discussion with another user to me, I'll copy paste what I wrote above, it really does seem as if you didn't read all of my comment: Simple scaling from Dangai Ichigo, profile could use some clean up though in my opinion. Took hits from a casual Post Mimihagi and SK Yhwach with Almighty off. Base Yhwach was casually High 6-A from the start of the arc. Yhwach got stronger after the first invasion due to the deaths of Quincy and Shinigami. Then Yhwach got further stronger during the second invasion with more deaths. Then Yhwach activated Almighty during his fight with Ichibei. Then Yhwach got even more stronger after absorbing Mimihagi. Then Yhwach got even more stronger after absorbing the Soul King. It's a lot of amps off a casual High 6-A from the start.
5-C Scaling
EoS Aizen / Muken Aizen:
Yhwach's casual AP at this point is 5-C, again I must copy paste: Hollow Merge True Shikai is 5-C and could hurt Post Mimihagi and SK Yhwach with Almighty off. A stronger and more durable Hollow Merge True Bankai Ichigo was casually ****** by Post Mimihagi and SK Yhwach with Almighty on. EoS Aizen no-sold an attack from that same Yhwach that was greater than what he threw at Ichigo in his past two modes that are already 5-C.
Hollow Merge True Shikai Ichigo was 5-C when he fought Post Mimihagi and SK Yhwach with Almighty off due to making that Yhwach bleed. That Yhwach was 5-C. Then Ichigo gets stronger as he enters Hollow Merge True Bankai which is higher than 5-C by an amount we have yet to apply. Yhwach then turns on the Almighty and casually defeats this higher than 5-C Ichigo. Afterwards, Yhwach absorbs Gerard, Haschwalth and this Ichigo's powers. The Yhwach that fights Aizen is vastly superior to the Yhwach that casually defeated a higher than 5-C Ichigo. Yhwach was casually above 5-C before an ever larger amp.
Plus, Yhwach was more serious against Aizen even, as Sigurd shows, where Yhwach is using larger attacks against Aizen then against the 5-C Ichigo.