Under the assumption of continuous, non-distinct damage:
- Rampart adds approx 4.4% mitigation.
- Inner Beast adds approx. 6.7% mitigation.
So Inner Beast beats Rampart by a big margin outside of psychological and mechanical considerations.
The psychological aspect simply refers to a persons compulsion to save CDs until almost absolute necessity, at the potential loss of average mitigation
The mechanical aspect refers to abilities, such as Mountain Buster and Death Sentence that give time different damage weights. This gives abilities with shorter durations/CDs a massive advantage as if 60% of the total damage only occurs in isolated times of 3-6s, then increasing mitigation outside of those intervals is inefficient and the average mitigation of the ability drops pretty drastically. Inner Beast absolutely destroys Rampart in this regard as you are free to use Inner Beast almost off CD and if absolutely necessary you are capable of falling on Infuriate for an instant Inner Beast.
Under the assumption of continuous, non-distinct damage:
- Sentinel adds approx 2.2% mitigation.
- Vengeance adds approx. 3.8% mitigation.
Same scenario as Rampart vs. Inner Beast. Better overall mitigation without considering psychological and mechanical issues and when you take them into consideration, Vengeance is much better than Sentinel.
I didn't mention it because Holmgang's worth is difficult to quantify. There are 2 scenarios to compare against with those 2 abilities:
- You've just taken a large proportional hit and without immediate heals, you stand a chance of dying. (Following a Mountain Buster/Death Sentence).
- You're taking massive continuous damage. (Caduceus /ADS)
In scenario 1. Holmgang is better. More likely to happen multiple times in a single encounters which makes the shorter cooldown more beneficial, also the reducing damage doesn't serve too much purpose as the damage outside the bounds of the ability is relatively small and fairly easy to heal.
In scenario 2. Hallowed is better. This is harder to quantify, but I would personally give it to Hallowed. This situation will usually not occur multiple times in an encounter and mostly happens towards the end , meaning CD has little worth. So the benefit here comes down to duration and damage mitigated as it provides a buffer for DPS to do whatever needs to be done (Kill Caduceus, Tank Swap ADS).
You cannot compare Storm's Path to either as it has the potential to be better than both simply because not all damage relies on STR and not all damage can be blocked. We cannot really discuss whether or not it is better because we have no idea how Storm's Path damage reduction is going to work as of yet.