Yes knights will become more tank. But same goes for all other vocations, it wont change anything on how good the vocations are balanced between each other.
For example.
Let's say druid is top damage dealer at the moment and can tank the most people with the right amount of soul orbs. After the extreme rune fix they will have lower damage like all the other vocations but will still be the top damage dealer. Now we come to the tanking part, a druid with the right amount of orbs, they can tank most so after a fix they will be even more tank like all the other vocations but still be the top tank.
And now to the part where I said mages will benefit the most from it. It's simply because of your huge amount of mana, everything but criticals is based on numbers so you will take the least overall % of damage. I will show it to you with a math example.
Let's say one sd does 10 damage and since the knight recieve a little bit less damage it will be 8 for him. A knight has 50 health and a mage has twice as much mana which means 100.
So let's see how many sds it takes to kill the mage and the knight.
Knight = 50/8 = 6,25 SDs
Druid = 100/10= 10 SDs
And since you are always talking about soul orbs and waste enableing you to do so, tank more as a knight since you heal much (25%) and keep in mind you have a huge pool of mana, why not enable knights to boost their health to the level of a mages mana ( with soul orbs of course ). That would make us able to tank more but with the same amount of waste. Seems fair to me since we are supposed to be the tanking vocation.
After a fix of the extreme runes, if they would do it, trust me you would be the biggest tank of the server.
Edit: Just to show you how extremely big your mana is, if I as a knight would want to have the amount of your mana rebirth 1834 as health I would have to be rebirth 2828,6.