yes but at the end of the fight with good devour i want to be at 90%-100% HP
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Devour also costs 65stamina and it's so easy to be under 65 using RoP
Need to change your mindset regarding HP on the Reaver. You don't need to be ending fights at 90-100% HP, you need to be ending them more like at 50%HP. This is partly why guard on hit is decent on Reaver, it is a refillable buffer that doesn't count against your damage bonuses from health loss. Alternatively, heal on hit is like getting cost reduction for Dragon Rage, and it allows you to transition back to an AOE weapon auto attack for pure heal if you get overzealous.
As others already mentioned, it is a good idea to get Charging Bull-> Gore and Trample and at the least tap it before you use Devour. That way the total stamina cost is only 10.
If you are going to use ROP, it needs to be used fairly situationally, and deactivated before stamina gets too low. You can do that manually, or just use CB to charge through someone to right outside the circle. I don't use ROP all that much, because I think on the whole it doesn't really increase DPS. It has the most benefit against a small group you can roflstomp quickly, which is pretty much a composition where you don't need higher DPS anyway. Against large targets, I would rather just dump stamina into CB and or Combat Roll. Or whatever else. But you can toggle it on in small bursts for a but of a bonus.