Yeah, this is true. This is a form of labor being contributed, it's just on a different scale. Of course it isn't the same as striking workers and their livelihoods, but it's also not as simple as categorizing it solely as gameplay.

FR's entire skins/accents feature, an extremely popular part of gameplay that contributes a great deal of appeal to the game, is driven almost totally by user-generated content. The artists are not monetarily compensated for the value they provide to the game.

The ethics of using user-generated content is actually something that's been discussed in other areas of video gaming and social media marketing, so this anon is on to something.