However, I could compromise my opinion on what I think should be the standard generation method if it could be show that rolling (edit: or standard array) as default is better for newer, and in particular, younger players.
I would have thought this was quite easy to demonstrate.
In order to understand the rolling method, a player needs to understand the meaning of the six stats. And that's it - he then just rolls and assigns the numbers to match up with his image of the character.
In order to understand point-buy, a player needs to understand the six stats as before, but also needs to understand the non-linear relationship between the points and the stats spent. And, indeed, to be any good at doing point-buy, he then
also needs to understand the relationship between the raw stat and the modifier that that gives you.
My experience with newer players is that random rolls are
vastly preferable. That said, it is possible that I just haven't explained the system very well.
(It's also worth noting something that I hadn't previously considered - which is that a standard array is better still for new players, as it removes one step from the process, and neatly eliminates the 'bug' of some characters being rolled better than others.)
All that said, though, I think 4e got the general approach right - present the three methods together without comment, and let people choose what works for them. (Where 4e fell down was in making the rolling method significantly worse than point-buy, but that's something 5e can easily fix.)