The RCP average is regularly gamed by the Dems and their fake news media wing. Like you pointed out, its basic math.
They look at the average and say, “How high do we need to make our next “poll” to get the average to rise by this amount?”
The they go out and manufacture a fake poll to meet exactly the figure they are looking for (oversample Dems by say 10%, oversampe blacks etc). Any 10 year old with basic math can do it.
Then they headline their next prime time “news” with the fake poll having Biden leading by 14 points plus a certain “insurmountable “ RCP figure. Then they repeat that all day in all their TV programs.
Its suppression polling 101.
The other thing that's come out recently, is that the pollsters are choosing as "Republicans" suburban single women (the weakest-for-Trump GOP voters) and totally avoiding rural Dems (the strongest-for-Trump Dem voters).
That way they can pretend the crosstabs reflect reality while still keeping their thumbs on the scale.
(Oh, yes, Blexit and the Hispanics for Trump phenomenon. Also the college kids forced to stay in Mommy's basement will not be simultaneously casting their Biden votes in two states at once; AND, indications of early mail-in ballots returned, suggest that Dems are actively cannibalizing their own Election Day turnout for the sake of optics right now. That's a sure sign of desperation and panic.)