That's the point, it doesn't matter. Enjoy any you want.
Todd just wants "his" Fallout games to be the most liked, to stroke his ego.
Also side note, sales never works as a metric because the gaming industry is constantly growing, any game released now sells much more than it ever would have 5, 10, 15, 20.. years ago. Regardless of quality.
It doesn't really matter for Fallout either, it's pretty basic at its core. It's not like he needs some deep understanding of the factions to play a character here. It's just a post-apocalyptic world, where his character happens to have no hair or nose. It's always been a sandbox, which lends itself well to a show.