Courage of Colossus greatly overshadows Grasp of the Undying and Bond of Stone
Even in Courage's nerfed state, it is still greatly more valuable than the other two. I'll seperate these into sections.
Bond of Stone Has such a marginal impact that you dont even know if its doing anything at all. Where in an average of a 30min game, you'll be lucky if it redirects even 500 damage total. That is an average of 16 damage blocked per minute. And the initial of 4% damage reduction for yourself is also non existent where it can be taken out of the game without anyone noticing the changes.
Grasp of Undying It had it's limelight when it both dealt and healed for 3% of your maximum health. Yes it was strong for it's time but with the introduction of Courage, it marginalizes it's purpose. Grasp was supposed to help tanks sustain throughout the lane phase and help those who lacked in damage. However nerfing that sustain away makes Courage all the more valuable.
In what circumstance would I ever want to choose Grasp or Bond over Courage? Is the issue that Courage is too strong or that the formers are too weak? Because I will be honest, I almost never used Grasp or Bond even before Courage came into play. I just find those keystones that weak.
Black Cleaver &
Frozen Mallet. It might even encourage these buys much more frequently among the ones who shouldn't build it.
Darius Main.
absolutely feasted against anybody with a ferocity or cunning keystone.
, but definitely use Colossus for all the others.

stripped of its aura because auras were hard to appreciate? Knight's Vow and Bond of Stone both do something similar to an aura: an always-on effect (on a target) that's difficult to gauge what the range is and difficult to appreciate just how much mitigation it's doing for you.