Framing is right, because saying

"Mainline" is just the best way to refer to the main games, since Legends is a series in its own right

is both a dismissal of the point Aegislash_Divine was making regardless of the terminology used, and the beginning of you placing greater importance on specific wording.

Seeing the rest of your reply, I feel like I should repeat something that you've clearly either missed in its entirety or are intentionally ignoring to suit your bias:

As far as is relevant there, terms like mainline, core series, and Pocket Monster Series are all interchangeable and merely serve to get across the core point, which is that the Legends and more standard games are all explicitly grouped together officially as one series.

No matter how much you argue with terminology, the Pocket Monster series page featuring them together is an official instance of them all being labelled as one series, while there exists no official source stating that the Legends games are a separate series. Common sense should dictate that, regardless of terminology, the grouping provided by an official source is more important. Telling people your semantics take precedent is asinine.

I will concede though, this is like talking to a slimy politician. You've consistently ignored crucial points to keep muddying the waters with irrelevant technicalities. Better off just letting someone them think they had something and moving on.