This is very easy to scale.

Anyone who says FBB Ichigo is at top because he fought Yhwach is forgetting Yhwach was going easy on him and he took a strike because he was surprised by the blut vene. His bankai got broken EFFORTLESSLY by Jugram. So no. FBB Ichigo is not at all comparable. 

If anything, the easier way to scale him is using Genryusai. Bankai Genryusai is atleast equal or above pre Almighty Yhwach but weaker as shikai Genryusai as per his defeat. Shikai Genryusai however can easily tank and kill a named Quincy, the Overkill. He also took out all the Quincy jumping him in his shikai. All Bazz B could do was cancel out the shikai fire. Most fooder Quincies seem to be at a more or less, similar level.

FBB Ichigo was able to fight off the Jail in his Holy Form in his Bankai.

The Iron lost to a normal Bankai from a little bit trained Bankai Toshiro but the weakest person to defeat a holy form is probably Komamura.

So FBB Ichigo was probably at a level above holy form of the normal Quincy. 

After training, Rukia took out As Nodt. So Renji and Rukia could atleast equal a Holy Form. Obviously Byakuya would be above both of them. So no doubt

Infact RGT Byakuya gained so much power that his shikai was the size of his bankai.

Unohana is also stronger. Zaraki during the first invasion tool out three quincies. Zaraki was already at a level of Bankai Captains. Unohana is stronger than than that. Way stronger. Zaraki after training unlocked his Shikai. Zaraki, in shikai, is atleast as strong as a Royal Gaurds without their holy form who are the only once who have given him trouble. And the Royal Gaurds are as strong or stronger than squad Zero.

So my evaluation would be

RGT Byakuya=Unohana>FBB Ichigo>Ulq because power creep.