Meryem took a Rose at point blank range, and he doesn't seem like he's ready for it (he certainly was surprised by it) and he didn't die immediately from the impact. There's no way any attack delivered by a human is even in the same league as what the Rose can do.
Let's say a guy has this ability that creates a wound that never seals, which would break all kinds of rules of fairness, and he was able to wound Meryem. Meryem would still have more than enough time to kill everyone and then he'd probably die a few weeks later from the wound. Remember, even grunt ants can survive for a day having their head severed from their body. There's no way the Royal Guard or Meryem is less durable than that.
Meryem ripped his own arm off to apologize to Komugi, and he didn't even need to use any technique (like what Netero did, for example) to deal with the injury. It's pretty clear he wasn't planning to kill himself over a game, so we can imply that at his level, losing an arm and its associated wound does not bother him. Note that this doesn't mean he takes no damage. Obviously he's down an arm in this case but the fact that he took enough damage to lose an arm doesn't actually slow him down at all. So there's no way you can open with a surprise attack and try to push for an advantage, because even if you took an arm from Meryem he suffers no penatly beyond having only one arm left.