Valve charges 30% for access to their marketplace, and allows you to sell Steam keys for your game at whatever price you want through your own sales channels, without paying Valve a cent.

I'm not sure how any of that is sketchy or gross. As far as marketplaces and platforms go, this is quite reasonable, and there are many successful games which are either not on Steam, or are cross-listed on multiple platforms, or are cross-listed on both Steam and the developer's own distribution channel.

I'll give you lootboxes, they are pretty shitty.