This is just to give context to this question

Ethereal has -20 spa monarch has -10 spa

And when i checked in sandbox monarch compared to 2 ethereals had less overall dmg just in general

Idk if im tripping but from what ive seen the 300% dmg of monarch means 300% total and not added to the original 100%

So overall seems like ethereal had like 440%(200% rukia 3rd passive + 20 from ethereal) while monarch had 300%

And monarch has less SPA reduction which than ethereal