2) the betraying node is not winning anything, because he's not making blocks at any faster pace than if he remained faithful to the other miners and their agreed-upon protocol.
wrong.. he has no competition so although his average times of maybe say 10.026.. he is not fighting off competition
ok
imagine it this way...
there are 2 100m tracks
track A
5 runners
they do their runs and after 100 races
on average each racer wins 20 races (give or take as some racers are slightly faster) but each race has a winner somewhere around 10 seconds
track B
1 runner
he runs, and after 100 races
he wins 100 races no competition
each race take around 10 seconds give or take a few miliseconds
he does not take 50 seconds.. he still only takes ~10 seconds but because he has no competition he wins every time
here il display it better

remember only the green numbers matter as thats the "fastest win", and there is no second place.. hense why no one cares about how long it takes the rest, which is where you wrongly think it takes the others much much much longer than reality(you imply he only gets 1 block every ~50 seconds)
as you can see.. on a track of 5 racers 1 guy only wins once out of 5 races..
but on his own he wins every race.. obviously.. and also it does not mean that if he only wins 1 race out of 5 with competition. that it would take 50 seconds without competition