Just because Hunt got knocked out by Manhoef (who isn't just "some middleweight" by the way) this is Melvin Manhoef we're talking about. Who, in 32 victories knocked out 29 opponents. If you think Lawler has a better chin than Mark Hunt because they shared a common opponent, or that because Ngannou hasn't fought Manhoef therefore he hasn't been knocked out by him makes him have a better chin than Mark Hunt, you need to rethink the line of thinking.
If you don't think Mark Hunt surviving clean Cro Cop head kicks in two fights or Roy Nelson eating a clean right hook by Lewis while out of position qualifies them to be in the discussion of having the best chin in MMA just because they were knocked out before, I don't know what does.