Do you have quantitative evidence of 10 million D&D players, because the number of players playing D&D today is probably much less.
In early 2017 Chris Cocks (President and CEO of WotC) estimated 9.5 million players. November 2017 was the best selling month of 5e.
nobody wants to suck at playing the game
Definitions vary. I surmise that the vast majority of players feel that they don't suck with any of the class, subclass, and race selections. The D&D player base is no longer confined to hobby game enthusiasts who spend their spare time thinking about the game. I bet most players only think about the game while they're playing it.
and also most games that people play D&D have more than one combat every four sessions as she claimed in her video.
You're moving the goalposts. I responded to your comment that D&D designers must cater to the 'extreme combat/powergaming' players. Replying that most players have more than 1 combat every 4 sessions is not a reply to that statement.
So if combat is more prevalent and people do not want to suck, then those players will adopt some powergaming tendencies to feel they are contributing to the group play.
I disagree with your premise and your conclusion. I think the vast majority of players feel like they are meaningfully contributing to the group regardless of their character choices. D&D is a cooperative game. Most players don't play to be in competition with each other.
Also I never claimed to "cater" to powergaming... only to include that style of play when designing the game....
You said that [designers] need to 'address the needs' of powergamers. 'Addressing the needs of' is literally the definition of 'catering'.
unless your definition of catering is including a style of play that you personally disagree with...then yes I guess I was catering.
This makes little sense to me. "Catering" is a verb. One can cater to a single person, a small group, or a majority. It means to provide what is needed or required to someone or group. My definition of catering has nothing to do with agreement or disagreement.
I do think that it is not in D&D's best interest to cater to a very small amount of its players by changing the game to go against its goals and thus alienate a large number of players.