GreyLord
Legend
FYI: Just because something counts as an attack, i.e. because you make an attack roll, for example casting a spell that involves an attack roll, DOES NOT mean you are taking the Attack action. I hope that clarifies things.
It's listed under the attack Action...as per...How to make an attack.
You may have missed it as I edited this in...
Edit: I would like to clarify something that is hinted at throughout the PHB, and even the DMG, and further clarified in the MM...it's what I've been pointing out. That there is a difference between Single Melee attack and when multi attack is possible. This is why Extra Attack SPECIFIES ONCE or that it works when ONE attack is taken. The MM also specifies that there are different types of attack actions, most normally as a melee weapon attack, a ranged weapon attack, or otherwise.
It is a DM decision, but a DM could determine just like the Sage Advice, and determine Multiattack is merely a new and different type of action (outside of those defined in the PHB or other core books). This would then also apply to Extra Attacks as well, as they are also very similar to Multi Attack and NOT a single attack. In that instance, I think it creates a bigger problem because then it's not a matter of whether Extra Attacks are an attack action or not, but whether it counts as another type of action, and how to or when it can be twisted to be utilized as such (Aka...could you do extra attacks as an action and a bonus action with Multi attack or vice versa or other attempts by players to twist the wording).
The problem when you discard the simple rule of what or what is not an attack action, is you open a bucket of worms as to what else can be squeezed in.
If an Attack action is NOT what the PHB defines it as...and instead is ONLY COMPOSED OF A SINGLE Attack....then the section in 192 under attack actions, where it states..
Certain features allow you to make more than one attack with this action...
Would in this light also be invalidated...as the same applies to the Multiattack from Monsters...especially in light of the wording for it in the Monster Manual.
but hey...
I'm not bothered with RAI or interpretations...
I'm just bothered with people trying to shoehorn their houserules as official.
I'd rule the same as many arguing that Extra Attacks don't stack with Multi Attack, but where I realize it's a houserule of clarification, others are presenting it as official rules.