About ownership - and this is just my feeling, not law or anything - I’ve always considered my GOG library games as owned. At any time, you can download 'em, burn them to disc or something and play them without the manager.
Conversely, stores like Steam, Uplay, Epic, etc … it’s definitely more like a ‘rent’ vibe. Like when you subscribe to a cable TV channel - you’re licensed to watch whatever you like, but the day the company shuts down - that’s it, ‘your’ shows are gone. Unless of course, you took time to archive them for your personal use later. The licence to view / use is temporary, not ownership per se.
I’m not technical minded, maybe there’re some games on Steam that launch without the manager, and for Epic, the same applies. Just saying how I personally feel when the word “ownership” is used here.
Also also, I wouldn’t be reselling my favourite games. I’d like to transfer licences to a friend who also like the games - say to a few of my wee nieces and nephews. For games I don’t use / like, it’d be cool to toss them out the Library and maybe pick up a few Steam Wallet coins for them. (Yes, I know some people have 25k games). Hey, Economics is complicated and there’s no such thing as a perfect system - again, just my little 2 pence. Cheers.