Bro, you've confirmed who exactly he is. You know he's a High Human. No need to beat around the bush saying "He's probably stronger than Schnee", just outright say "He's a High Human". Even without knowing which of the High Humans he is, or even if he's one of the ones from before the Dusk of Majesty or a new one, if someone with at least room temp IQ hears that, they'll know that messing with him is a big no-no.
He's not "Oh, he's pretty strong, but we have Throwbacks of our own that can probably handle him" dangerous, but "If you have any plans that involve messing with the people, places, or things he's invested in... scrap those plans, or put them in a safe with the label do not attempt until the High Human named Shin is confirmed to be dead WITHOUT our intervention. DO NOT TOUCH SHIN EVER UNDER ANY CIRCUMSTANCES for your descendants to maybe get to in like 500 years" dangerous.
He's not a walking calamity - walking calamities fear him... no, they don't necessarily fear him, but they do fear the things he leisurely hunts on a whim to make joke gear.
Playing it down like that is a great way to get overconfident fools to do something stupid to piss him off.