GOG and itch’s approach to preservation is always gonna be limited by legality, you can’t keep a game on your platform if the publisher requests its delisting; ofc piracy isn’t constrained by this, so it’s inherently better at preservation

at least, since the games on there don’t have DRM, once you have them you keep them (and with GOG, you can also download offline installers that you can reuse on any computer you want). they make piracy (and therefore preservation) way easier in that way, because pirates don’t even need to repack the game!