Not as much as you would think. Most Ronins follow the pattern below:
Melee after emptying Leadwall at close range followed by Arc Wave followed by melee. Most players tend to run everything empty without worrying about defense. Which is a big mistake cause Ronins are veeeeeery fragile.
Problem with Ronin's melee is that it doesn't have pushback. And despite what it may look like, it does the exact same damage as a regular punch.
If a Ronin that is NOT under the effects of sword core is in your face and you have the 5 way splitter equipped, do not melee him out of range but simply dash backwards. Bring your shield up to soak up a bit of damage from the lead wall, dodge the incoming arc wave and let him have it with the alt-splitter rifle mode.
The reason why you want Ronin up close is because Ion's projectiles can miss if she is far away. If all 5 of em hit him continuously and nail some critical shots, Ronin's health will plummet like an anchor during freefall.