They weren't one match away from being first in the group, they were one match short of making it out of the group.

In 2016, TSM went 3-3 while SSG, the eventual 2nd place team in the whole tournament, was 5-1 in their group with a 2-0 record over TSM. Even if TSM had won one of those games against SSG, they wouldn't have been first in the group unless they also won a tiebreaker match.

And in a format where you play only 6 games, a single win is kind of a big swing, especially against the top team in the group. In 2017, if G2 had beaten SSG even once, they would have advanced and knocked the eventual tournament winners. But instead, they went 0-2.