@Riot Strength of the ages may have needed nerfs, but the other defensive keystone needs buffs.

When was the last time you've seen Bond of Stone or Grasp of the Undying? Whenever I play, these keystones have been largely replaced by other keystone, as they are simply better. The champions who occasionally take them are usually supports (and those are very few) or champions that can't make use of Cotc.

Why do they need buffs?

The other keystones simply fill their role better or give more utility. GotD is split between damage and sustain. However, the damage amount is quite small and so is the sustain. Thunderlords outclasses it in damage and because the sustain is barely noticeable, it's pretty much just simply better.

I think Riot intended Grasp to be a laning keystone. It does fulfill that role. However, it becomes virtually useless later on. The solution to this is to have it scale with level. Have it heal 1.5% at level 1, 2% at level 6, 2.5% at level 11 and 3% at level 18 or something. The damage could also scale up too.

Also, i'm not really sure what to do with Bond of Stone. I think the best way to change it is to make it more into something distinct from Knight's Vow, or even change it entirely.