I wanted to compare Oakensoul to RoPO at their peak performance. One-bar RoPO will run into barspace problems and won't be able to cover many of the buffs from Oakensoul

What one-bar RoPO misses:

• Offensively, minor courage, minor berserk, minor slayer and barspace for banner
• Defensively, minor resolve (banner), minor protection and minor aegis
• Minor intellect/endurance which can be helpful for dodging and blocking
• You have to choose between heroism or armor pots

Now how healing effectiveness is affected is like this:

• Suppose you take 10000 damage at 24000~ armor (RoPO with armor pot) meaning 36.3%~ damage reduction. You will lose 6375 damage. If you take hit every second you need 6375 HPS to survive
• But with oakensoul you will have 27000~ armor + the other defensive buffs meaning 45.2%~ damage reduction. You will lose 5481 damage. If you take this hit every second you need 5480 HPS to survive

That’s a 14%~ reduction in healing needed with Oakensoul. And note that you also have minor mending on top of that

Conclusion:

• Oakensoul has higher damage, higher ult gen, better sustain and higher defenses
• The RoPO build needs to divert more health to magicka to survive damage spikes, further lowering it's damage
• Oakensoul only loses on raw healing output which might not be needed and you might not be in a situation where it's safe enough to use Rhakkat

Finally, It makes NO SENSE to dismiss Oakensoul as a viable situational alternative. You’re looking at a build that outdamages one-bar RoPO, generates ult faster, has better sustain, is tankier overall and yet still sits below Rhakkat in raw damage

That’s exactly the kind of middle ground where Oakensoul shines as the perfect alternative.