Whis stated UI Goku's power was at the bottom of what the Angel's techniques are capable of, so he's probably at best equal to pre-revival Merus. I wouldn't say him having power and speed equal to Moro after stealing Merus' abilities and then overcoming him makes Goku superior to Merus when Moro stole the abilities of a Merus struggling to maintain his existence and it was quickly made apparent he couldn't control such a Ki. In a scenario where his existence isn't on the line, Merus would win through either his power or superior experience with UI.