No I get what you are saying, I just don't think you realize how influential constant power is. It is the whole Aura effect all over again. Auras tend to be removed because they have to be incredibly overtuned to make up for how weak they feel.
Old Taric is an excellent example. Shortly before his rework he was considered one of the 5 worst champions in the game. Yet his ult could be active more often then it was down, did damage, and granted over 12k gold worth of stats to his team. It was one of the most ridiculously overpowered ultimates in LoL. Most people didn't realize this because his ult felt weak since it was little more than an aura.
In the same way Knights Vow has a lot of power, you just don't notice it because it isn't obvious.
Lets look at some math though.
Knights Vow:
Cost: 2300
Raw Stats Value: 1764
About 77% Gold efficient.
Locket:
Cost: 2200
Raw Stats Value: 1680
About 77% Gold efficient.
So what can we conclude? Base stats are equally gold efficient and thus not worth comparing. We only need to look at the passive effects.
Knights Vow:
12% damage absorbsion + 12% healing from bonded's damage.
15% Bonus movespeed towards bonded target.
40 armour when near bonded target.
Locket:
70-665 shield, 90 second CD, does not stack, reduced locket effect for a short time. Decays over 2.5 Seconds.
We can assume that since both these items are ally reliant we can run them both in optimal situations to compare them.
Ok lets get into the nitty gritty details.
We are assuming these are both operating under ideal conditions, that means you are near your bond for knight's vow and grouped as 5 for locket.
Knights Vow:
15% Movespeed = 592.5 Gold
40 armour = 800 Gold
Damage reduction/healing to be discussed.
Locket:
Now there is no gold efficiency stat for shields, but I think taking the gold efficiency of health and dividing it by it's uptime is fair right? Logic is that you have that much health for that much uptime.
665 health shield X 5 targets = 3325 health. This has a roughly 3% uptime. However during that uptime we lose 100% of the shield. Therefore the actual amount of shielding per second we get is half that at 1.5% uptime.
We get roughly 50 health (rounding on the generous side) gold value from a locket shield on 5 targets every 90 seconds. This means that the active on Locket is equal to 133 gold.
Of course that is just looking at the raw statistical uptime value of Locket's shield, realistically it has more worth by virtue of being an anti burst mechanic. In regards to that we have what I will assume is a more generous way of calculating it's value.
Locket provides 3325 effective health gold value per cast. This is meant to counter burst. Lets take AP since that is the common AOE burst form that locket is best against. I would say Brand's ult is the best example of something locket is designed to counter right? Brand's ult has a 125% AP scaling and 1500 base damage total.
We can take the base damage off what the shield negates (3325-1500 = 1825 shield left) 1825 shield vs a 125% AP scaling. So for every 1.25 AP worth of gold we can call that equal to 1 point of shield. That means the shield is worth 1460 gold of AP, or 31,755 gold.
Now that is a lot of gold value, but we left out a few things. The shield decays over time, which means that on average (especially vs something as delayed as Brand ult) we only get half the shield value per cast. That lowers us to 15,878 gold of shield.
Funny how looking at the same thing different ways can give such different results right?
That leaves us looking at the items like this:
Knights Vow:
Base stats + armour passive + movespeed passive = 3157 gold value
That is 137% gold efficiency so far.
Locket:
~800% gold efficiency under ideal circumstances.
However I don't think that is fair. Locket does, like it or not, have a CD. That CD matters. So I think we still need to apply that 3% uptime to the gold value because it matters when you don't have locket, and it matters a lot.
So 3% of that 15,878 gold value active is equal to 476 Gold. Better than calculating the health uptime by a lot, but still not all that impressive.
Locket (again):
Base stats + active (with uptime included) = 2156.
Just under 100% gold efficiency.
Of course the calculations will differ depending on the ability you are using to calculate it's gold value. I used Brand since that is the biggest general reason to buy a locket IMO as it hits all 5 targets and has a pretty good AP scaling.
So we can see that in terms of gold efficiency Knights Vow actually wins out even without having to do that damage taken/healed passive which is wonderful because I have no desire to math that shitfest out.