It’s irritating when people say that the only reason Jon & Arin started a “Let’s Play” channel was to “jump on the ‘Let’s Play’ bandwagon” like a lot of the other popular Youtubers did. The difference is that Jon & Arin were actually active in the gaming community ASIDE from playthroughs that anybody could do. They were both part of “Did You Know Gaming?”, and each had their own video game review shows as well: Jon had Jontron Show and Arin had Sequelitis. Even before Sequelitis, several of Arin’s Egoraptor cartoons focused on video game characters and themes. Not to mention they’re both huge fans of AVGN, who also goes more in-depth about the history of games and the video game industry than the average Youtube Let’s Player like Tobuscus, PewDiePie, Smosh, etc.
Therefore, it makes SENSE for them to start a channel that focuses on them playing video games. It’s not like they had completely non-game-related channels BEFORE Game Grumps and then suddenly decided to start a gaming channel just ‘cause everyone else was doing it, unlike the bulk of the popular Youtube Let’s Players. They showed genuine passion, knowledge, and professionalism toward the gaming community before Game Grumps even existed, so I think the fact that they later started a playthrough channel together was inevitable and not an act of “selling out” in the least.