iserith
Magic Wordsmith
well I guess no one can claim anyone is misreading or not using the rules since the maker of the game agrees with it...
I can and do regardless of what he said. As far as I am concerned, he too is overlooking the importance of page 66 with regard to players being the ones who determine how their characters thinks, act, and what they say. This section taken with the rules for ability checks tell me the DM may describe how a monster tries to intimidate a character, but the player says whether or not the character is intimidated.
The tweeted response doesn't even make much fictional sense. A monster is trying to intimidate you so your response to its intimidation tactics is to try and determine its true intentions by reading its body language (Insight)? Or to attempt to influence it with tact, social graces, or good nature (Persuasion)? Also, he references "Diplomacy," which isn't even a thing in D&D 5e - I'm being charitable by assuming he meant "Persuasion." I don't see how either of these ability checks apply in any blanket sense.
I could see a player trying to read a monster's body language and mannerisms to determine if the monster is actually a threat, but this is an action on the part of the character to gather information to make a decision in the face of the DM describing the monster's attempt to be intimidating, not an opposed ability check to avoid being "intimidated." The monster's Charisma (Intimidation) check might then oppose the character's Wisdom (Insight check) as a way of setting a DC. This would be consistent with the rules in my view.
In any case, if that particular designer and his players (or anyone else) like to roll dice to determine how a character thinks or acts, then they should keep at it. It will never be something I do at my table.